If you happen to be staying in a hotel in a room next to mine, it is very likely you would hear parts of my upcoming speech bellowing through the walls.
Even after the enormous number of presentations I've done I still practice my stories and various bits of material the night before my event. I heard Zig Ziglar saying that he does the same thing.
Unless you are speaking every day, it is almost impossible to stay razor sharp with your delivery. Being a keynote / large event speaker, I may go 90 - 120 days between times when I tell certain stories on stage. The last thing I want to do is flub up a line or bumble through a piece of material because I hadn't thought about it for a couple months.
Don't get cockey! Practice your material several times right before you do your speech and you'll have a much greater chance that each word will come out perfectly.