I tend to agree with ImOpen to an extent; a lot of bad can certainly come from defining your life's purpose, if you're not doing it right. Note: I did post what I perceive to be my current purpose in annie's thread. I also wrote it, then, on the spot. I don't stand by it, but it was a good description of my feeling on it at the time.
A lot of people who say, "I don't know what my purpose is," I think, don't really have that exact trouble. I don't think they'd be better off knowing their purpose, except that the process of finding it might kick them out of what stupor might be bogging them down in the first place. In other words, coincidence, not causation.
A rule I'd suggest: if your purpose ever seems to be confining, ditch it. Personal freedom is important. So if you ever catch yourself saying, "I'd like to, but that's not my purpose," then some reconsideration is in order.
I suspect this is why many of the purposes people put down are extremely broad. You can't be confined by chains with you-sized holes.
