A friend asked me if I thought people who were driven by an actual purpose or intention of making the world a better place (however the purpose-driven defined a better place) actually did make the world a better place. This is sort of a statistical question, and since people can either outright die before ever implementing anything and/or implement evil things (like the mass murdering communists) I'd guess not. Additionally, many of the innovations and scientific breakthroughs we enjoy today are the result of accidents. Now, one can argue that the innovator or scientist had to have enough purpose to be doing something in the first place, which I suppose is true, but then you have to add in all the purposeful people who go and blow themselves up accidentally too.
If we severely limit the pool of purpose-driven people to those people whose purpose is morally acceptable, then we can at least assume having a sense of purpose is beneficial to one's self-esteem. Perhaps a healthy ego is highly beneficial in terms of quality of life, especially in adverse conditions, but that doesn't translate into making the world a better place. I think there is a different class of people who do make the world a better place: relationship driven people.
Parents are driven to improve conditions for their children.
This is the model whether husband, or brother, or missionary. The point is not the purpose. In fact, a purpose can get in the way, blind you to the needs of the person. Purpose can lead to long distance thinking. You can build a city that is uninhabitable. People inevitably ground thinking to the here and now, the incremental, the mundane. Purpose driven people get impatient, upset, call vast swatches of America bitter and stupid because they won't go along with their "awesome" plans. The relationship-driven person doesn't do that because his focus is on the other person in the relationship, and he trusts the bigger picture to God. Get enough relationship-driven people together, and you'll see some truly miraculous things happen.