The absolute best boost to my self esteem is to decide that something is going to happen and then making it happen.
Because I said so.
When I'm at the difficult stage, when I have something new to do and start to panic that I won't be able to get it done, the best antidote is hearing the voice of my colleagues saying 'if this was me struggling, what would you say to me'? You would say 'you have got this, you have done things you didn't immediately know how to do.' It will be fine.
You eat the elephant one bite at a time.
DColleague knows the signs when I am having a wobble, as I do for her. Having someone who absolutely understands is priceless, I can easily conjure up her voice.
Remembering previous challenges which I have overcome really helps. It always feels 'this is too difficult' when I am in the middle and yet, I always find a way forward. Sometimes, the way forward is 'this isn't possible, we need to find an alternative way forward'
Hope you find what works for you.