I spoke with a reader yesterday who was wondering how he can concentrate on his mission when he doesn't have one and doesn't even know what he wants it to be.
My advice was to begin by assisting the missions of others you respect, admire, or whose missions you find worthy of support. Most men are not leaders; most men cannot be leaders of other men anyhow since if everyone was a leader, there would be no one to lead. The social hierarchy is a pyramid, with fewer captains than lieutenants, and fewer lieutenants than soldiers.
So, find your mission by becoming a soldier. Over time, if you prove yourself useful, capable, and interested, you will become a lieutenant. Most men will be content in either role; only gammas and alphas naturally seek leadership and no good leader truly enjoys it due to the burden of responsibility for others it imposes upon him.
This is particularly true of sigmas, who don't seek leadership, but often find it being thrust upon them regardless of what they want. Gammas, of course, inevitably turn out to be a disaster whenever they manage to thrust themselves into a leadership position since they don't even accept responsibility for themselves, let alone for anyone else.
Anyhow, if you're not sure about your mission, go find someone who has one and offer them your assistance. Not me; I have no shortage of high-quality lieutenants and soldiers. But there are many good men out there who are in need of your help in moving their missions forward. Help yourself by helping them.