occam's razor

In the philosophy of religion, Occam's razor is sometimes applied to the existence of God; if the concept of God does not help to explain the universe, it is argued, God is irrelevant and should be cut away (Schmitt 2005). While Occam's razor cannot prove God's nonexistence, it is argued to imply that, in the absence of compelling reasons to believe in God, disbelief should be preferred. However, this is only true if and only if it is demonstrable that belief in God requires more and/or more complex assumptions to explain the universe than non-belief, as it could be argued that the non-existence of God would necessitate other assumptions.

From someone on Wikipedia.

simple, not simpler.