Those Who Do Not Learn From History...

History has much wisdom to impart to an avid scholar, or even to a hobbyist, who takes the time to actually and honestly listen. It can teach what approaches work best in different situations, as well as those situations that should be avoided at all costs.
Most of all, history teaches that things aren't always what they appear, and even a sure victory can fail. "History writes with very crooked lines." No exceptions. No "get out of jail free" passes. Learn from your mistakes, never make the same mistakes twice, but also never ever assume that just because "it worked for me the last time" it's going to work again. And never assume that just because it looks like something is going to happen, it is guaranteed to happen - because if you assume that, chances are you will be wrong.
Many mistakes in history have been made because the person making them assumed a result that didn't happen. These can be genuine mistakes, but even genuine mistakes can be just as deadly as careless ones. Never take anything for granted, always do your best even if you're told you don't have to, and above all never assume a victory in any circumstance - you'll most likely end up with a mouthful of bitter defeat, at least in the end. One assumption too many can cause anyone's downfall.
Plan ahead. Be prepared. And do your best.