Are you saying that the purpose of doing things just to do them is to give one self worth? I can agree to that as long as there is a goal, something to strive for. Just doing something and not measuring success is meaningless.

The question seems somewhat ambiguous. Need purpose for what, exactly? Sustaining biological function, a sense of satisfaction, or something else?

If it is any consolation, every willful action is purposeful toward accomplishing some goal. Therefore, every sentient, acting being has a self-determined purpose.