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.

Convicts in isolating will develop suicidal tendencies by a longer period of isolation, because they no longer have any stimulation of their senses. Also they will go insane, therefore it's by law decreeded they can only stay in isolation for a limited period of time.

For many they don't need a greater end goal, or greater achivement to work to/for. If you look at many housewifes their daily routies of cleaning, cooking and washing makes them happy and forfilled, sure a precentage will not like this and strive for greater goals, that they are suited for.

I don't go to the movies for a greater purpose, just to relax, social interaction with friends, etc, it's for stimulation of my senses.

You should try isolate youself for ? an year, no phone calls, no walk in the park, no TV, no radio, job ..etc.
You will get bored out of your mind, you will go insane.

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.