It is the thought that the least efficient way of of finding either happiness or pleasure is to pursue them. Put in terms of happiness, we can see it like this: To be happy you must quite literally "lose yourself". You must lose yourself in some pursuit; you need to forget your own happiness and find other goals and projects, other objects of concern that might include the welfare of some other people, or the cure of the disease, or simply in the variety of everyday activities with their little successes and setbacks.