Almost 20 years later, he's still not sure why. Some things just get into the head of a 3-year-old.
It was Aug. 23, 1992, and Vavra's family was at Mount Rainier in Washington. Tanner's father, current Twins hitting coach Joe Vavra, was managing Class A short-season Yakima in the Dodgers' organization at the time and he was spending a rare day off with his family.
Joe, his wife, Lisa, and two sons, Tanner and baby Treysen, headed to one of Joe's fishing spots. Tanner was to keep his fingers in his dad's belt loop so Joe and his mother, Lisa, could keep tabs on him. In an instant, Tanner broke the rule and headed to the car as Joe cast back his pole.
By the time Joe noticed, he was midway through his cast and couldn't stop. The hook caught Tanner's right eye and he spun around and fell to the ground.
For Tanner, that's where the memory goes blank.
For Lisa and Joe, it's still clear as day.
Joe put cold water on the wound. Lisa panicked and, in the middle of vast mountains, screamed for help. The family rushed to the car and drove to the hospital.
"I just held Tanner in my arms, and he fell asleep. It wasn't painful, but he knew he was hurt," Lisa said. "I just held him."
Tanner woke up in the hospital. He underwent four surgeries and had a contact lens placed in his eye. Tanner wore a patch over his good eye to strengthen the bad one and, after several years, his right-eye vision was 20/25.
Then came a backyard football game during a birthday party in 2000. Tanner played ... and was poked in his right eye. His contact broke, sending pieces throughout the eye.
The doctor said Tanner's eyesight would return. He didn't check the back of Tanner's eye because it had never been an issue. A couple months later, still blind in his right eye, Tanner went to a specialist.
Tanner's retina was detached. He would never regain vision in his right eye.
If it had been discovered earlier, the retina could have been reattached, Lisa said. His vision could have been saved. But things seem to happen for a reason, Joe says.
"Sometimes you don't know what that reason is," Joe said. "It seems pretty devastating at the time, but then you end up finding out there's some positives that come out of devastation."
Today, Tanner is a junior second baseman at Valparaiso. He led the team with a .327 batting average and 15 stolen bases, and ranked third in the nation with 20 sacrifice bunts. Last week, Tanner was named First Team All-Horizon League.
On one hand, it's easy to wonder what kind of player Tanner would be if he had two good eyes. On the other, there's no question his childhood incidents have greatly impacted him.
After all, a person with one eye succeeding in baseball? Yeah, right.
"I just use it as motivation, really," said Tanner, a right-handed batter. "I want to prove people wrong."
For a while, Tanner was among his own doubters. He saw numerous doctors and had so many men in white coats tell him what he could and couldn't do that he started to believe it himself.
Joe put a stop to that.
On one doctor's visit, the Vavras were told Tanner wouldn't have depth perception without his right eye. That's when Joe cut in.
"'I was a professional baseball player. I can throw that ball as high as I can and he'll catch it every time. Why is that if he doesn't have depth perception?'" Tanner recalled his dad saying. "That kind of stuck with me, where, you know what? It's not affecting me, why let somebody tell me I can't ever try to succeed because of it?"
Tanner's family helped, too. They wouldn't let him use his eye as an excuse.
Kids are making fun of you because your right eyelid is barely open? You're better than them on the field, Tanner's grandpa told him.
Got blindsided in hockey? It's hockey. Everybody gets hit hard.
"They didn't let me feel sorry for myself. No matter how cruel [people] were," Tanner said. "Obviously, that had to hurt them a little bit, too, but it's just tough skin. You learn to deal with it."
Joe and Lisa wanted their son to grow up with a strong will. But they were realistic when it came to baseball. They figured reality would set in around high school, where the game got a little faster. Maybe then he would quit.
He kept playing.
Two things in Tanner's life have been constant. One is that he's always had to prove himself. The other is that he's always succeeded.
He went to Madison College when he wasn't offered a Division I scholarship after a stellar career at Menomonie (Wis.) High School.
He spent a summer with the Alexandria Beetles of the Northwoods League, one of the top amateur wooden bat leagues in the country, and eventually earned a Division I scholarship from Valparaiso.
Valparaiso head coach Tracy Woodson and his staff were mostly interested in Tanner because they thought he could change the team's attitude. He has, helping lead Valparaiso to its first conference championship since 1979. After winning the Horizon League Championships on Sunday, the Crusaders also are on their way to the NCAA Tournament this week.
Tanner has accomplished Woodson's original objective. What he's done on the field has been a plus.
"I've had other coaches this year that have seen him in our conference say they can't believe he's doing what he's doing," Woodson said. "What he's done ... I couldn't imagine the player he'd be if he had two eyes. I've caught trying to close my eye and try to imagine doing the stuff he does, and I can't. I can't imagine."
It's been said that hitting a baseball is the hardest thing to do in sports.
Whoever said it probably had two good eyes.
Sometimes Vavra and his roommates, first baseman John Loeffler and third baseman Elliott Martin, take batting practice on their own.
"We'll joke around, and I'll switch around and hit righty and I'll try to close one eye," said Loeffler, a left-handed hitter. "It's tough."
"I just touch the ball. Like foul it off," Loeffler said.
"I'm lucky if I make contact," Martin said.
When Madison head coach Mike Davenport called to recruit him, Tanner was honest. He told Davenport he was blind in one eye. The coach had no idea.
It's difficult to tell when watching Tanner play, as proven by his accolades. The strength of vision in his left eye -- which ranges from 20/10 to 20/16 -- also helps.
One thing does stand out: How Tanner catches pop flies. Wilson said Tanner catches the ball low on the left side of his body, instead of above his head. The reason is simple: Tanner can't see the ball if his glove is above his left eye.
Other than that, he's basically just another player.
"It's pretty crazy," Loeffler said. "You know he can't see out of one eye, but then you're out there and you can't even tell."
Last year with Madison, Tanner took a bad hop in the face. The ball hit the protective Oakley glasses he wears and gave him a black right eye. Tanner played the next day, and people who didn't know his story were amazed he was in the lineup because his right eye was swollen shut.
It didn't matter, of course.
As Tanner advanced to play for teams with more media coverage, the various interview requests bothered him at first. He didn't mind talking about his eye, but it was repetitive.
It took Joe a while, too. He can talk about it now, acknowledging the more they talk about the "family scar," the easier it becomes. The family prefers to look at it in a positive light.
Because of the various stories written about Tanner during the past few years, he's received emails from coaches who wonder how he got to where he is and how other kids blind in one eye can do the same.
Joe says Tanner can be an inspiration. Tanner is hesitant to use that word because, in a sense, it highlights the shortcoming his family never let him use as an excuse growing up. But now, at 22, Tanner realizes he can use his platform and be a role model.
"If I can help somebody that way, or if I can help a kid that's trying to go through the same thing, I'm more than willing to do this stuff and I'm more than willing to talk about it to whoever," Tanner said.
Lisa says Tanner doesn't like to refer to his blind eye as a disability, which, for all intents and purposes, it is. She knows he's coming around to it, and since he's reached Division I and now the NCAA Tournament, he'll no doubt garner more attention as his story reaches an even greater audience. She hopes, in time, Tanner's tale will be able to fuel others who might face a similar situation as they chase their dreams. For now, Tanner is still chasing his own.
He wants to play pro ball. That's the goal, he says, when you're playing Division I.
Woodson, who played with the Dodgers from 1987-89, said Tanner is the type of player who will get tested at every level, should he get the chance.
That's all Tanner is looking for. A chance.
"I hope somebody gives me the opportunity, because I'll make sure to work my butt off to make them look good and make people realize it's not a disability," Tanner said. "It's just something that makes me a little different."
There have been players who made the Majors being a little different.
Jim Abbott was born without a right hand and threw a no-hitter with the Yankees.
Pete Gray, who lost his right arm in a childhood accident, played 77 Major League games in 1945.
Tanner has done his research. There have been one-eyed pitchers, like Tom Sunkel, who pitched in the National League for parts of six years in the 1930s and '40s, and Whammy Douglas, who pitched for Pittsburgh in 1957.
But as far as Tanner knows, there has never been a professional position player with a blind eye.
"I'm the first position player, that I know of, that's trying to follow in those footsteps and trying to go to pro ball," Tanner said. "I kind of want to pave the way a little bit for position players."
People will say it can't be done, that there's no way a person blind in one eye can play professional baseball. Tanner will hear their doubts, use them as motivation and try to prove them wrong.
Just as he's done from Little League to Division I baseball.