Hello, welcome to my random thought. This is my first article, so please, argue, debate, and enjoy.
As the headline state, this is about trusting oneself but not in self-help ways. I don't think repeating "I can do it" 100.000 times can do any good. I'm talking about fulfilling self-promises. I do agree that self-trust is crucial though and I will try my best to articulate that idea here. This is a draft for my thought so it will not be orderly, sorry in advance.
That's the problem most of us have, I can confidently say so. we make promises to ourselves, to live healthy, to work out, to do something good but then nothing happens. Most of those promises are more like wishes. But that behavior is devastating. we lie to ourselves, we are lied by ourselves, and we get resent, bitter by that paradox. One thing for sure, getting lie to and betray is not good at all.  

The more I think about it, the odder it gets. Many times I fought a situation when one breaks a promise to self in order to fulfill a promise with another. Why? Is the self not important? And more important, how can one be so naive trusting such an insane senerio? Like "I will run 50km a week from now on, go on diet, learn German and Japanese,..." yeah, good luck. Try saying that to another person, they will assume you're drunk. Yet time after time after time, we trust that. Because after all, that's ourselves who make the promise. most people are naive when dealing with themselves, I dare say more than 80%. There is no harm done to anyone, no damage to our reputation and it feels good for a while. So why not, let's make a bun of impossible promises and get high on them for a while. But what is the consequence then? Can you still trust yourself after so many lies?
In dealing with ourselves, that behavior builds up a personality the both naive and malevolent, both weak and cruel, vengeful yet powerless. That's just fuck up. I feel scared of my though sometimes.    
Let's expand that idea a little bit more. Can you trust other people when you do not even trust yourself? That's I don't know yet and I absolutely don't want to find out. Imagine feeling doubt about everyone and everything, that's like living in George Orwell's nightmare.
So okay, no matter how tempting it is, don't make a promise that's you can't keep even to yourself. Be trustworthy.