A simple phobia is an unreasonable fear prompted by a single object or situation.
A complex phobia may have clear origins, but it quickly escalates, introducing multiple and varied factors to creates a spider's web of internal chaos.
In a purely golfing sense, most competitors at the US Open suffer from a complex phobia: they spy the initials "USGA" and their brain goes into meltdown, a frenzy of anxieties about 520-yard par-4s, lots of them, narrow fairways, distant fairways, impenetrable rough, rock hard greens, fast greens, slopey greens, double bogeys, triple bogeys, big scores, missed cuts, Mike Davis, nightmares.
That's a lot of mind matter to untangle.
Brooks Koepka has identified the championship as a simple phobia and with it cleared his mind.
"It's pretty simple," he said after opening the 2021 event with a 2-under-par 69.
"It's a lot simpler than what guys make it. I think a lot of guys make it more difficult than it needs to be. Just got to understand where the flag is, what you're doing and where to miss it."
The proof is in the pudding: Koepka won the 2017 US Open, he won it again in 2018, in 2019 only Gary Woodland beat him, last year he was injured, this year he's two shots off the lead in a tie for fifth at the end of Thursday's action (the first round was delayed by morning fog and will be completed first thing Friday).
"I've just got a good game plan," he said. "I'm focused, I know what I'm doing, and I don't try to do anything I can't.
"It's just all about discipline in a U.S. Open. That's I guess the gist of it.
"Look, you're going to make mistakes out here, but you can't make double bogeys. If you can limit those to just bogeys, you're going to be all right
He scratched two bogeys on his card, but atoned by circling four birdies. He sits two shots behind the leaders Russell Henley and Louis Oosthuizen (who has two holes of his round remaining).
"You can't win it today but you can definitely lose it," he concluded. "Pretty pleased. Not the best, but I'll definitely take it."
Let's take a closer look at his US Open and Torrey Pines records, plus catch up with the rest of what he said after his Thursday round.
Koepka in the US Open
Somewhat surprisingly, this is set to be his second-best start in the championship.
He was tied fourth after 18 holes in 2017, but has otherwise never been better than T16th.
It's also worth noting, that, with the exception of his tournament debut in 2012 (when he missed the cut with two scores of 77) he's always made a move in the second round.
In 2014 he carded a 68 that moved him from T16th to tied fifth (he finished the week tied fourth), a year later a 72 eased him from T52nd to T44th (he improved all week to T18th), and in 2016 he confirmed he would stay around to land T13th at the weekend by posting a Friday 69 that vaulted him from T80th to T35th.
And in those last three more recent and stellar performances the pattern has repeated.
Two back of the lead in 2017, a second round 70 earned him a share of top spot ahead of a four shot victory.
He opened his (ultimately successful) defence in 2018 with a 75 for T46th, but a Friday 66 got him back in the game (tied fourth)
And two years ago he was again T16th after 18 holes before a second round 69 drew him up to tied sixth and right back in the reckoning.
Koepka at Torrey Pines
He has a poor record in the Farmers Insurance Open, going T41st-MC-MC.
Moreover, it's actually worse when you look at his South Course efforts: 74-74-74-72-72.
His opening round is therefore not just a personal best there in competition, but comfortably so.
Koepka on his fitness
"Feels good. I feel great. Movement is as good as it's ever been. Strength is just getting stronger and stronger every day. It's not going to be anywhere near 100% for a while, but it's just creeping closer to that number every time."
Koepka on his first round
"Happy the way I putted the ball, a lot of confidence in it. Started pretty much everything right on line where I wanted to. I'm not the most comfortable with poa. I don't enjoy putting on it, just because the ball can bounce off line so many times.
"But I'm not very pleased with the way I drove the ball on the back nine. Everything just kind of leaked a little right and then over-adjusted on seven and hit it left. Shouldn't be too difficult, just go figure it out, might be alignment, ball position. Usually something pretty simple."
Koepka on last year's US Open
"I didn't watch a shot. I was actually out here in San Diego just doing rehab. Rented a house for two and a half months, something like that. Didn't watch any of it, but I don't watch too much golf in the off-time."