It's an interesting question, perhaps one you don't take too seriously until you reach a certain age or point in life. I USE to answer that question with "Some Day". But a funny thing happens the older you get. Your life gets more complicated with responsibilities and circumstances, and your world starts to spin faster and faster. And you know what? You just never seem to arrive at that magical "Some Day". Go ahead and admit it, we all know that "Some Day" is code for "it just ain't gonna happen".
"Some Day" I'll lose weight, I'll take photography more seriously, I'll learn Italian, I'll travel to every major league baseball stadium, I'll start a blog, I'll learn to say "no", I'll live where I want to live, I'll learn what is and what isn't in my control, I'll zip line, I'll participate in a tri-athlon, I'll learn to not care so much what others' think about me, I'll be happy.
"If Not Now, Then When?"
Sometimes you need a spark to set fire to your procrastination. Maybe that is the purpose of a mid-life crises...time's a tickin'...your demand for "Some Days" might be greater than the supply (Econ 101 did come in use after all). And you make the startling realization at how fast time really DOES fly...wow, it really isn't just a stupid expression my parents use to say. Instead of asking "if not now, then when?" You ask "why not NOW?". What I have discovered is that taking action is a terrific drug. It's addicting and a definite mood enhancer. They should bottle it. Heck, I'd set up shop and sell it on street corners. Alleviates fears and the blues too.
Interestingly enough, I have also found that some of the things I pursued, just aren't what I want after all. Good bye tri-athlon...I'm satisfied and happy with what I've accomplished on my own, I've found I don't need to actually be in a race except against myself. And some things, no matter how hard I try to pursue, will probably be a never ending quest. Where's the fun in being perfect anyway? :) But that's okay...I'm active in the pursuit instead of not even starting it yet. Where I am in my life right now, pretty much the only thing that limits me are my resources, not my inaction.
If not now, then when? "Some Day" is today. I just wish it wasn't on a Monday before I had my coffee.