I've found that the best way to do this is to make "values the truth above everything else" be the core of your identity.
Then you can let yourself peripherally identify with other things, and, when they're challenged, your core will step in and let you deal with the challenge rationally.
But doing that is even harder than it might sound. I've been explicitly working on it for a couple years now, and although I've made progress -- I think I care about getting the truth more than I care about avoiding embarrassment now, for example -- I'd still probably religiously defend myself or my loved ones if either were verbally attacked rather than try to figure out what truth the accusation contained.
Then you can let yourself peripherally identify with other things, and, when they're challenged, your core will step in and let you deal with the challenge rationally.
But doing that is even harder than it might sound. I've been explicitly working on it for a couple years now, and although I've made progress -- I think I care about getting the truth more than I care about avoiding embarrassment now, for example -- I'd still probably religiously defend myself or my loved ones if either were verbally attacked rather than try to figure out what truth the accusation contained.