The greater good.

Locke: Why don't you trust me, Sayid?
Sayid: For one thing, you've been carrying a gun you've told no one about.
Locke [taking the gun out of his pocket and giving it to Sayid]: We found one of the smugglers about a half a click West of here dressed as a priest - Nigerian currency in his pockets, and this. Now you're armed and I'm not. Does that earn me any trust?
Sayid: You gave this to me because I caught you concealing it. That earns you adaptability.