Question about thoughts in General

I always hear your thoughts are not your thoughts, you just have thoughts. There are helpful, unhelpful, good, and bad thoughts.

If someone has the thought ” I am ugly” we can say you are having the thought you are ugly but it doesn’t mean it is true. If someone had the thought “I am beautiful” wouldn’t that still hold true, that you are not your thought but it does not mean you are?

How do you decide that you are in fact the particular thought? Do our thoughts just come down to which one you want to believe, and whether or not its helpful to believe? I am trying to put things into perspective without going so philosophical here in the road of “I think, therefore I am”
OR is it more like.
I am ugly because xyz…..
And I am beautiful because of xyz…

Putting the circumstance of a recurring thought in the model
C-  Brain offers thought that I am ugly
T- This thought must be true
F- Sad
A-  Uninviting, head down, shrugged shoulders, negative behavior, not smiling,
R- Create evidence that I am ugly

C: Brain offers thought that I am beautiful
T: This thought must be true
F: Confident
A: outgoing, smiling, friendly, positive behaviors, inviting,
R: Create evidence that I am ugly.

Nothing so its not about what you do to show beauty, just the energy and behaviors that are demonstrated internally and externally based on how the person feels.

If we talk about opinions and say “xyz’s opinion doesn’t matter its just your opinion.” If your opinion is negative about yourself, how can we say your opinion about yourself is all that matters if your opinion about yourself is the one that is leading to the feeling and result you don’t want to have?

Please help here.