How do I transform my investment thesis from analysis to confirmation bias?

I have been doing this seriously for about three years. I read 10-Ks, build my own DCF models, and listen to every earnings call for the names I follow. The problem I keep hitting is that once I am mentally invested in a name (before I am financially invested), I can construct a beautiful narrative for it. The bull case feels airtight. Then six months later something breaks the thesis and I look back and realize I was selectively weighting evidence the entire time. For people here who have been doing this longer, how do you actually keep yourself honest? Do you write a pre-mortem? Do you keep a dedicated section in your thesis doc for 'what kills this'? Do you only buy after a peer has poked real holes in the reasoning? I am asking about the actual mechanics, not the principle of 'be objective.