What is the most important thing to know? Some people think it is to know if there is a God or not. Some think that it is to know that science has the only answers that are important. Or that the physical world is all there is. What is the meaning or purpose of life? These are big truths that need answering. But I propose that there is a truth that you need to know before all of these. If you ignore this truth, all other truths (or beliefs) that you hold may be wrong or arrived at by mistake.
Here is the most important thing you need to know: we see the world not as it is but as we are.
Why is this the most important thing to know? Because we don't see reality, the world, the universe, simply as it is. We are biased. Let me say this again louder. We are biased. We cannot help it. We are made that way. All that we think and how we evaluate evidence to come to conclusions are the result of living our lives up to now. We don't hold our beliefs...there is a God, or the opposite, the physical world is all there is, on pure evidence that we have accumulated rationally.
Human beings are not rational creatures, even though we like to think that we are. That is another false belief most of us hold, but there is plenty of research showing this is true. My friends that are atheists have come to this belief, and it is a belief, through evidence that has been put together based on something else other than a rational system. And the same goes for my friends who are theists and believe in a God.
We can see the same things and come to different conclusions all the time. Look at the political landscape these days. Liberals think conservatives are crazy, or worse. Conservatives think liberals are crazy, or worse. And we live in the same country, exposed to basically the same things, but we filter out the evidence differently. So we see the world differently. We see the world not as it is, but as we are.
This is so important to know. First of all, if we realize this we can hold our beliefs not so tightly. We can be open to take in evidence better. Know that what you see is not simple truth, simple reality. We have an inner filtering devise. It's not important to try to get rid of it, just know it is there.
Secondly, knowing that our filter, our mind and emotions, changes what is real to something else, we have to know that what it is we are seeing is changed by who we are. We can't help it. It is in our nature. I've had incredibly loving parents. It's easy for me to believe in a loving God, a safe universe. If I had been brought up in a dysfunctional home, chaotic, maybe I would start my search for reality from a different place using a different filter for my evidence.
I am not arguing here for either realities. I am saying that unless you understand this, most likely what you believe in is distorted by your life experience. We need to know that we are wearing a filter, then, and only then, can we begin to look at the evidence around us and try to understand our world. To do it without knowing that we see the world not as it is leads us into error and probably a waste of precious time.