If Jon was secure about himself he wouldn't keep popping for PEDs against a fighter he's already beat, or use cocaine and alcohol to make himself feel better. He's talked about this at length.

And if Izzy was secure about himself he wouldn't talk all kinds of straight cringe shit against a fighter who was doing nothing but treating him with respect. Robbie is a great example of someone who is completely secure - didn't need to talk trash to build himself up, is humble in victory and defeat, and even though he had every reason to be salty that Izzy treated him like trash for the entirety of the build-up, he isn't.

Look at someone like Ronda, who was so insecure that after Holm beat her she literally dropped off the face of the planet despite being hyped to the moon and back.

You're naive if you don't think that insecurity and doubt penetrate the most talented and successful people in our society.