That depends on what you mean by "believe in ourselves." If you mean, "Do we have confidence in ourselves," then some of us do, and some of us don't, just like everyone else. If you mean, "Do we believe we exist," then, once again, the sentiment is similar to everyone else, that being that we generally believe that we exist, and anyone who thinks otherwise are outliners. Atheists are just regular people who just so happen to not believe in a god.