It's often said that we're all born atheist.
Imagine - you're 3 or 4 years old, and the concept of God has never occurred to you. You are without a belief in God - the classic definition of atheist.
Then someone tells you about God, and you, being an obedient child, adopt the concept as an operative description of the world. Your belief in God might be 50, 90, 99 percent or more certain. (For the sake of realism, let's assume that absolute certainty is impossible, but that you will have some non-zero, non-one-hundred percent certainty in any proposition being true.)
As you grow up, your education about God ebbs and flows. If you have a devoutly religious family, and travel in devoutly religious social circles, you may tend to become more certain that God is a true proposition. The opposite may also pertain, that your family is not devout, even agnostic or atheist, and based on your own experiences and personal make-up, you will become more or less certain that God is a true proposition.
I've followed that second path, although the journey was not a straight line from 90 percent certainty that the concept of God is real to 99.999999 percent certainty that the concept of God is not real.
One aspect to our perception of reality is also how we define things. For instance, I am virtually certain (99.999...%) that Yahweh doesn't exist. He never appears, he never affects the world in a notable way, in fact, he's described in the one holy book that asserts his existence as incompetent, inconsistent, ill-tempered, petty, violent, and arguably the biggest murderer in history (Genesis chapters 6 thru 9). If he exists, he sounds like someone that we should terminate with extreme prejudice.
I'm less certain that a pantheistic concept of God does not exist. But. A pantheistic God, a God that we are part of, has different implications for my life than does a theistic entity such as Yahweh. One, I cannot discern the difference between "Pantheo" (or whatever we'd call this thing) and nature as it's been manifest to me throughout my life. Two, there's no doctrine, rituals, narratives or other trappings of typical religions that might have an affect on me. It really has no impact on the world.
Given these two conceptions of God (of many possible propositions about the world) it still makes sense to behave as if there's no God.
Pascal was a pussy!