I always thought it was about cards: "Play the hand you're dealt, not the hand you wish you had" but I could be wrong as well.
Edit - Ah, I was close. "You play the cards you're dealt." (no second sentence) was popularized by Charles Schultz through the comic strip Snoopy, of all things, but it certainly pre-dates him. The term referring specifically to card playing dates at least back to the late-1700s (and almost certainly earlier, that's just the latest print usage easily found) and as a non-gaming metaphor to at least the mid-1800s (and, again, probably earlier but that's the oldest confirmed print reference).