Everybody makes the decisions of life based on probability, not certainty. Basic logic shows that the side of an argument which is supported by the most evidence is the one most worthy of adherence even if that support isn't to the level of absolute proof. Same goes for scientific theories. Faith only becomes the prime factor in decision-making when one has an insufficiency of facts. The more facts one has, the less faith is needed.
Religion relies on faith since it has so few facts.
Science is the exact opposite. For example, a person about to cross a road stands on one side, looks both directions, collecting the evidence necessary to determine the probability of making the journey across in safety. He can never be 100 percent sure he will make it. He could have a heart attack or be swallowed by an earthquake. The lack of 100 percent certainty doesn't keep him on the side of the road, however.