There is inherent in D&D, and other paper-pencil RPG’s, a social gaming contract. That is to say, that we’re gathered at this table in the spirit of teamwork. Though inter-party conflict can be rewarding, woven into the tapestry of the game is the idea that each party member serves a distinct purpose(s). Each of us is a valued member of the team, and none of us can do this on our own. I understand that the DM may be asking you to suspend your disbelief, here.