Why is it so hard to convince myself of something that I logically know is true?

Because the heart disobeys the head. We delude ourselves and deny the truth in order to avoid pain. But the faster you face the truth, the sooner you can heal your heart and give your mind the peace it craves.

It is because, for some reason, somewhere deep in your mind you feel a bit unsafe and insecure about it

It's one thing to reason out something, but it's another to truly believe it. Belief is a combination of both logical reasoning and emotion; together, this forms the overarching rationalization for our actions. Even if something seems "logically true," you still need to rationalize the truth within your heart.

Sometimes our emotions, may block our logical side. Feelings may keep us blind. Therefore instead of our minds/ brains, we let our heart mostly decide the way. And we can not control it any time we want. Those times it's hard to convince yourself by only logic, unfortunately. Cause your heart needs more sensitive reasons to believe / to be convinced. But it is not something quite bad to be honestly, cause it's our nature, shows that we're human. And don't forget no matter which one -your heart or your brain- speaks louder, the last decision will be always yours.

Why it is probably too hard is maybe you overthink it. Or, you are so stressed out about this something that you need to be a bit more light-hearted.

I always thought it was because it was something you didn't want to believe. Yes it logical, but the truth would be painful, so your mind won't allow it to be true to protect yourself.

Because belief and emotion often overpowers logic. For example for me I know that going on a walk will result in a good time with my daughters logically. However for some reason anxiety makes me feel like the only outcome is a horrid accident. Yet logically that is super super unlikely with how closely I watch them. So the problem isn't flawed logic, it's what feeling is driving your disbelief.

It's hard because sometimes we really don't want to believe or even want the fact to be true. But perhaps unfortunately it is. At least you have identified the first step - that you know that it is true but you're having a hard time accepting it. #simplesmallsteps One step at a time, identify what's stopping you from convincing yourself and try to seek subsequent remedies.

Insecurity? Too much knowledge? Mistrusting? May I ask what you are trying to convince yourself of? For me I can find any and every logical reason why someone shouldn't love me, or why they should abandon me.

A small part of you is fighting against the idea for some reason. Sometimes the head fights against the heart. Question why you feel that way and discuss how you feel with someone you trust.