On the whole, you don't tend to know when something you're enjoying is the last one you'll have. You probably don't know what your last meal is, unless you have a date with the state. You don't know what the last time you'll laugh is, the last orgasm, the last moment of happiness.
You don't, but I do.
Not yours, don't bother asking. My own. I know exactly when my last laugh, last meal, last breath, will be. And it's not for a long time, so it's a blessing, really.
I do know!
Fine, shoot me!
Um, ok, maybe not...