Why do OCD irrational thoughts feel believable despite being false?

So im not a scientist or anything, but I remember reading something that essentially said that people who don't have OCD, when they experience an intrusive thought, they are able to pass it normally without caring. However when it comes to people with OCD, the thoughts trigger our fight or flight and essentially we react the way we do because of our disproportionate anxiety levels due to the disorder. My psychiatrist explained it like imagining a tube where the thoughts flow through. Now for OCD, imagine that tube is broken due to our chemical imbalances, sending the wrong signal everywhere, instead of smoothly like its supposed to, causing chaos. It's like that. Also personally i feel like, OCD is very good at masking itself as natural with false feelings, more rampant intrusive thoughts than a normal person, thought loops, groinal responses, etc. Really, who WOULDNT doubt themselves experiencing stuff like that on a daily basis?

I think a lot of things that are involved in OCD have to do with our nervous system and unconscious parts of our mind. This is like the part of our brain that is "ancient" and sometimes doesn't help us in the modern world.

OCD is also referred to as the Doubting Disorder. It usually goes after our identity/core beliefs. Think about it, most ppl with OCD or even on here say things like “I don’t want these thoughts, did I do this on purpose, what if I actually like this, I feel guilty having these thoughts”. It’s because the thoughts are going after the persons core beliefs because they DO NOT want to be associated with even the thoughts or ever want to commit the acts. WE do not want to be those things and afraid we are. So we usually look for reassurance and or develop the compulsions to help keep the thoughts at bay and our identity intact. Non OCD ppl do experience the same thoughts we do. However it’s at a lesser extent because they are able to dismiss them and not focus on the uncertainty of their identity with the thoughts. We need absolute certainty and that’s what scares us is the “what if it is me” thought process. BUT it is not us. Also, the science behind why it feels so real is this: thoughts and emotions are connected. Always have been always will. You constantly think of positive thoughts you are very likely to be happy. You constantly think of negative thoughts you are very likely to be distraught. Now, when you enjoy something(food, movies, time with friends, a gift) that triggers good emotions which then will trigger good thoughts. Visa versa for the opposite. As OCD thought process we ruminate and obsess about negative thoughts (even if in no context they will be good, they are making us feel guilty in context) which usually makes us feel ashamed, anxious, terrible ppl. Now when a thought pops in that is “woah I never thought of it this way, what if this is true” it’s the OCD/imagination coming up with new angles and or logically discovering angles to destroy/doubt the identity. This will make us feel negative because it’s an unknown and OCD ppl thrive on certainty to protect their identity.