Write your own appraisal?

My friend told me his manager asked him to fill up his own appraisal form himself. He don't have any idea how or what to write. If he write all the good stuff, then the management might think he's not honest, not telling the truth or over confident. But if he writes something bad about himself, then the management might think he's not good enough for the position.

Hmm, this is a tricky one. How should he write? In fact, how can his manager asked him to write himself? Appraisal form should be filled up by both the manager and the staff, write about how this staff performed throughout the whole year. How would my friend know whether he's performing well or not (well, everybody thinks they performed well what...) right?

I asked him to write something good about himself, such as I'm responsible, hardworking and blah blah blah and write something which he thinks he needs to improve, maybe to be more socialize, more friendly and etc.

Have you ever write your own appraisal before? If yes, what did you write about yourself?