People believe in God or they don't. Some say they don't know, but if they don't know or are not sure that God exists, then they don't really believe, do they? But if a person does have belief in God, it is not based on any kind of empirical evidence. It might be based on personal evidence, which is not allowed when doing science. It might be based on a trust in others who have told them that God exists. It is certainly, at the root, based on some authority (like the bible). But any belief in God can never, ever, be based on reason or data, because no empirical data exists in support of the God hypothesis.
Using the methods of science, there is no way to prove that God does or does not exist. The scientific method uses inductive reasoning, which means that even though most theories can never be proven 100 percent, one can collect so much evidence in support of a theory that it is treated, for all practical purposes, as a fact. In other words, it becomes useful at predicting things in the real world. When one hypothesizes the existence of God, and especially a specific god with certain personality traits, then the empirical evidence in support of this hypothesis is so scarce, even non-existent, that it can be completely ignored as a possibility.
So to compare, science does not always get the right answer, or what is closer to the truth, the complete answer. But, unlike religion, science corrects itself. That is the method of science. Science is unbiased, non-judgmental, data-driven, and most importantly, skeptical. A good scientist doubts everything until the evidence is so compelling that it can join the ranks of the most highly-respected theories, such as atomic theory, quantum theory, or the theory of evolution. On the other hand, religion, including Christianity, is based on authority texts (the bible, the Koran). They are driven by feelings and emotions. They are most certainly biased and agenda-based, and highly judgmental. More importantly, a religion cannot be skeptical of itself.
Now, in every aspect of daily life or business life, most people embrace the more rational, data-driven path to problem solving. Only in their religious life do they embrace faith - the blind, authority-driven, emotionally-charged path that defines their religion. Those who claim they are certain that God exists, especially the personal God of the bible, are certain only because they have decided to be. They have nothing external on which to base that certitude. On the other hand, science would never claim 100-percent certainty that God does not exist. It would claim only that the evidence in support of God's existence is so minuscule and rarefied that it need not be considered for practical purposes. The evidence in support of God's existence is exactly the same as the evidence in support of leprechauns and unicorns. Those creatures might exist, but nobody takes that possibility very seriously. Thus, although God has not been disproved, he is relegated to the extremely-unlikely-to-exist pile and forgotten about, that is until some fundamentalist waves him in your face again.