Imagine the disappointment of a major leaguer failing to tag up on a fly ball for a run that would have won the game in the bottom of the ninth.
Consider the despair of an NFL offensive tackle jumping offsides on fourth-and-goal at the 1-yard-line with seconds remaining and his team four points behind.
It happens. Marcos Ambrose knows how they feel.
Ambrose made the mental blunder of his career two months ago when a first Sprint Cup victory was within his grasp on the Infineon Raceway road course.
The Tasmanian driver was leading under caution in the closing laps when he needed to save fuel. He turned off the engine, but did so while moving uphill and had trouble restarting the motor.
By the time it refired, it was too late. Jimmie Johnson won the race, and Ambrose finished sixth.
"Sure, I still have nightmares about it," Ambrose said Tuesday. "I got greedy trying to save too much [fuel], and we cost ourselves a win. It was a fundamental error; no doubt about it. I had a pretty hard couple of days getting over that weekend.
"It's fine now, but no one will give the race back to me. The race is gone. I prefer not to talk about it anymore."
Ambrose insists he's only looking ahead. He can't change it, but he can make amends this weekend at Watkins Glen (1 p.m. ET, ESPN). The historic upstate New York road course is his best track, a place where he's always a threat to win.
"We have unfinished business, and we have our best chance to win this weekend," Ambrose said. "We'll be a player. It would be very special to all of us if we can sneak a win in on Sunday."
Ambrose has moved on from the Sonoma incident. He also is moving on from JTG/Daugherty Racing and the No. 47 Toyota at the end of the season.
Ambrose and team officials announced last week they are parting ways. Bobby Labonte will drive the car in 2011.
And Ambrose? Nothing definite. Reports suggest he could replace Kasey Kahne next year in the No. 9 Ford at Richard Petty Motorsports, but he hasn't ruled out the possibility of returning home Down Under and racing again in Australia.
"My heart is in NASCAR, to be honest with you," Ambrose said. "I feel like I've become part of the sport, but I haven't become a contender on a weekly basis.
"I have taken a risk right now. I have jumped out of the team that I had fully sponsored and I was contracted to drive for 2011. I don't have any contract on the table to sign. So there is a risk involved with that. I understand the risks, but I would love to stay in NASCAR and finish off what I started."
Ambrose, 33, appeared well on his way to future success last year when he surprised most observers by finishing 18th in the standings and posting seven top-10s in his first full season in Cup.
But 2011 has been a big disappointment. He ranks 28th in the Cup standings with only two top-10s, one of which should have been a victory at Infineon.
Johnson was as surprised as anyone to witness what happened that day.
"It's the last type of mistake I would expect to see," he said after the Sonoma race. "You can kind of count on mistakes with some guys. I just didn't really think that he would be the one to make a mistake. To see the mistake happen as it did was totally off the wall. I don't know if I've ever seen that eliminate a guy from winning a race."
It was one of those moments every athlete fears: a rare bonehead decision with a potential victory at hand.
No one expects to see it happen again, and no one on the track Sunday will underestimate Ambrose's chances of winning on the 2.45-mile road course.
Ambrose has won the past two Nationwide Series races at The Glen. He finished third in his first Cup race there in 2008 and was second to Tony Stewart last year.
If there's anyone better at Watkins Glen than Ambrose at this point in his career, it's Stewart. He has five victories on the seven-turn course in the past eight years.
"It is going to take us beating Tony," Ambrose said of his chances. "He has won so many times there. We have to match up against him and shadow his lap times and have a good strategy to stay in contention."
One other driver who's pretty good at The Glen is Jeff Gordon, who has four victories there, but the last one was nine years ago. Gordon and Ambrose participated in a Goodyear tire test at The Glen in June and swapped rides for a few laps.
"He got in my car and went really fast," Gordon said afterward. "I got in his car and went slow. He's a good guy and a heck of a road-course racer."
That he is, which is why the Sonoma miscue was so hard to swallow.
"It's been a rough road here the last couple of months," Ambrose said. "I feel like if we can get a win for [the 47 team], Watkins Glen will be our best chance."
Ambrose is one of the favorites to win Sunday. The key is not to beat himself. Just don't turn off that engine going uphill.
Terry Blount is a senior writer for ESPN.com. His book, "The Blount Report: NASCAR's Most Overrated and Underrated Drivers, Cars, Teams, and Tracks," was published by Triumph Books and is available in bookstores. Click here to order a copy. Blount can be reached at firstname.lastname@example.org.