I’d ditch that pansy-ass ‘box of chocolates’ metaphor in favor of a more realistic one:
“Life is like a line of waiting taxi cabs pulled up to the curb in front of a fancy hotel. You never know which raving lunatic is going to get you to your destination – or for that matter, whether you’ll get your destination at all.”
— end of line —
Or…
How’s about this one…:
“Life is like a vaccuum cleaner. If it doesn’t suck, something’s wrong…”