You're on the start line. Heart pounding, nerves wrecked. As soon as the gun goes off, you're already jittery and slip your pedal. Now you're losing spots and frantic. Desperate to not lose places at the onset, you make risky moves sprinting back to the front; you touch wheels with another rider and go down. Maybe you're an hour in, and you flat out of the front group. Frazzled, you quickly try to change the flat, and over zealously blow the tube, losing another 3 minutes, or more. Or perhaps you go out a bit too hard, red line the first few climbs to stay in contact and get behind on your nutrition. Instead of catching up, you just start over. 3 hours in, you're way behind on calories and imploding. That's a race ender.
Racing is as much about mental fortitude as it is about physical fitness. What you do when you get a mechanical, when things don't go to plan, or when the unexpected strikes, can make all the difference between winning and a DNF.
Part of preparing to race, is visualizing what you're going to do in any circumstance. Come up with a plan of what you will do if you have a mechanical, go too hard, crash, run out of nutrition, are in the lead with 1k to go; everything you can possibly think of. How will you respond? What will your reaction be? By visualizing and deciding on a plan now, you can easily avoid disaster later. Better yet, practice some of these things. Structure workouts around going too hard before settling in. Practice fixing flats quickly, or experiment with nutrition to get to the verge of a bonk and bounce back. Knowing how to control your emotions, and like a robot, right the ship without getting worked up, can literally save your race. And sometimes, keep you in contention.
It doesn't matter who you are, everyone gets nervous at times for racing. Nerves often lead to poor decision making. When you are prepared and mentally ready for any circumstance, you will be ready and able to cope with those issues that arise, and move past them, putting them out of your head. That might be the most important part too...
I've had lots of races where things didn't go my way. But really, they didn't set me back much. The problem was I thought about them the rest of the race, and they demoralized me, discouraged me, and kept me from performing at my best. On the flip side, you may be having the ride of your life, and ride too hard in your excitement and blow your lead. Maintaining control over your mind and emotions is absolutely paramount to putting in your best race.
It takes incredible discipline to be able to put these kinds of hurdles out of your mind, to control your emotions adequately in the moment, but by visualizing the good and the bad and practicing them, you will set yourself up for success on race day.