What do you mean, "be true to yourself?"

"Above all, to thine own self be true," said Polonius to Laertes in Hamlet. People say it today: be true to yourself. It's a consolation: "Hey, at least I was true to myself." It's a barb: "You're not being true to yourself." It's a maxim.

What is your self? Should you always be true to it? What if your self needs improvement in some area? Should you be true to the self all the time? Doesn't the self change?

Maybe an improvement on "be true to yourself" would be: watch out for your own ass at all times. That makes it a little more concrete, doesn't it?