It happens so many times. Once you think you know something, it turns out there’s one more thing and reality is different than what you thought.
Here's a nerdy example. Let's say a you learn all about triangles and pretty soon you're using that knowledge to develop a new branch of mathematics called trigonometry. Then, it dawns on you to use trigonometry to navigate the broad flat ocean and you're on your way. After many days, You're completely lost! What went wrong?
Soon after your misadventure, you learn from a prominent astronomer that the earth is round. It suddenly dawns on you that you used the properties of flat triangles to navigate a round world. You need to use spherical triangles. You incorporate spherical triangles into the new math you've been developing and set sail again. This time you arrive at your expected destination. You confirmed the world is round and successfully applied a new branch of mathematics in one stroke! What a day!
Our understanding of the earth and trigonometry didn't progress like this. However, this nicely illustrates there's always one more thing and reality is often different than what we thought.
Living without God is like living a flat life in a round world. God is that additional dimension that doesn't make sense on one level but brings clarity to everything else.