When discussing beliefs unsupported by evidence (the existence of god(s), bigfoot, ghosts), believers often throw out this trope: "The absence of evidence is not the evidence of absence." And they're absolutely right! I can't say "We have no evidence of X, therefore X is not a real thing/phenomenon." However, this point-in-time analysis of the evidence misses the fact that evidence is not static, nor is the nonexistence of said evidence.
To illustrate this, let's consider a hypothetical machine that consists of a hopper filled with an infinite number of ping pong balls, attached to a launching device; at the other end of the room is a device that collects the balls as soon as they fall. Once a second, a ball is launched toward an observer, who has never seen a ping pong ball in the past. The first one launched is plain white, the second white with some writing, the third white with writing, the fourth plain white, etc. The observer watches these balls each day for 16 hours, but they're always shooting by, even when he's not looking. That's 57600 balls he sees, and 28800 balls he does not see, every day.
The Observer's Conclusion
By the end of the first day, the observer is confident that there are ping pong balls with at least a dozen different writings on them, but they're all white. It's not a stretch for him to assume that there are more than a dozen things that can be written on ping pong balls, but even after one day -- and 57600 balls -- he figures that he should've seen at least one non-white ball by now, if there were any in the hopper.
But what if the non-white ones happened when he wasn't watching? He certainly must've missed at least a few during blinks or in periods where he was distracted. Plus, a whole third of the balls in the hopper are going into the collection mechanism, never to be seen at all! He clearly can't write off the existence of non-white balls.
Each day, he sees at least one or two balls with writing that he does not recognize, so -- as before -- it's easy for him to assume that there are more writings than he has previously seen. Given that there are an infinite number of balls, he's growing more confident that there are, in fact, an infinite number of things written on the balls as well. This is not a stretch; it's a natural extrapolation from the evidence he has collected. However, every day means an extra 57600 balls he's seen, and by the end of the 100th day, he's seen nearly 6 million different ping pong balls, and every single one is white.
So when we ask him if he believes there are any non-white ping pong balls in the hopper, his answer is a quick and resounding, "no." This, like the conclusion, is a natural extrapolation from the evidence; it's just inverted.
You experience reality continuously, not in one second 'packets' like our hypothetical ball observer, but it doesn't change the fact that you are collecting new evidence every single second you're conscious. And for every negative observation you make on subject X, it becomes less likely that a positive observation will ever come. You can't say that there is an absolute, unquestionable lack of X, but you can say this: based on everything I know, X does not exist.
We have no direct evidence of god, despite around 6000 years of recorded human history. While it's possible that we've just missed that ball -- or it just hasn't filtered down the hopper yet -- it becomes less likely with every observation we make. On a long enough timeline, the likelihood converges to zero.
It's been long enough.