I’d say both shifts in mindset is a tactical decision. Sometimes you really need to have faith in yourself to achieve something. Sometimes you need to remove your ego to sustain something. Every situation is different, but I would agree one should not give up tactical options in the greater strategic battle of coping with life and the onslaught of dealing with people.
Practice. Relinquish a belief and deal with the fallout (internally with the psychological hit to the ego, modulate the impact it has on you), then strive for something that may or may not be achievable (and modulate again, not letting the attainment be your everything, and not letting failure be overly impactful).
It’s tough when you’re insecure because your primary mental fortification is an inflated ego. Just get used to (practicing) inflating and deflating the ego (ideally just keeping it half filled with air) so you literally are not a zero-self-esteem mess out there in the world.
If you have no practice with this, every time life gives you an opportunity or challenge, you’ll make judgement mistakes.
