Nothing really.  I think being certain about anything is a sure fire way to be wrong.  So I am never certain about absolutely anything.  I also take nothing for granted or think anything is going to last forever.
Every day I face it with the uncertainty that I will make it to another day, so I spend every day doing things that I love and I need to do as opposed to the things 'I think' I should do or 'I think other people think I should do.