It has nothing to do with aggression. You will be pushing your self....maybe not the first day because it will be more structured, but your subsequent times, depending on your exuberance level....you will. When you are pushing yourself farther and farther, you will eventually find the limit. The track is as addictive as heroine. It is much safer than the street, but that doesn't mean crashes, (or even mechanical issues) occur less frequently. Quite the opposite. It means that when it does happen, it usually results in far less damage to person of machine, and there are corner workers, spotters, crash trucks and, if need be, ambulances.
Riders are usually segregated in groups according to their experience and speed (A, B and C). You would start out in the C group, and be with others who are moving at a similar pace. But believe me, the faster the group doesn't mean more crashes. Again, quite the opposite, The A group usually has the fewest number of crashes. B group actually has the most problem because they have gotten over the timidity and are starting to push harder than they are able. Not trying to scare you. It's just that the purpose of a track day isn't to putt around on a Sunday drive. It's to have fun and go fast...faster than you ever have on the street! If someone is going slow, sometimes they can be more of a danger.
You hone your skills, absolutely!! But how do you do that? By going at a pace that pushes (not stretches, mind you) your comfort zone. Once you are comfortable there, you push a little farther, and so on. That's how we develop any skill. At some point, a mistake will be made. Usually, that might result in a quick slide, or chassis bobble, that you recover and keep going, but you do have to be prepared for the mistake that results in picking the bike up off the deck. And at the track that is all it is. There are no trees, telephone poles, on-coming cars, or cell phone drivers. You dust yourself off, fix the bike and anticipate the next time you can get back out there and practice not doing what you did the last time.
But all the crash talk aside, fatigue and dehydration are a big problem. You won't realize how much exertion you are putting out...until afterward. I usually will go through a gallon of water and two quarts of gatorade in a day! Plus, without some shade you NEED to have a hat that keeps the sun off you, at a minimum.