Experience taught me that it is not so much about trusting yourself that you'll do the right thing (because nobody can know what the right thing is in advance) but about willingness to give yourself a chance to make mistake and learn from it, and to stand by your decisions whatever they are.
So, you could say that I trust myself to be confident enough to pull through everything that might come as a consequence of my potentially bad decision.
The worst thing in my opinion is not standing by yourself and taking advice from someone against your own. If things turnout to be bad, than you might blame someone else but in the end you are the one who has to live with them, so the consequences better be the ones that are the product of your decision than somebody else's, even if they are bad for you.
So, you could say that I trust myself to be confident enough to pull through everything that might come as a consequence of my potentially bad decision.
The worst thing in my opinion is not standing by yourself and taking advice from someone against your own. If things turnout to be bad, than you might blame someone else but in the end you are the one who has to live with them, so the consequences better be the ones that are the product of your decision than somebody else's, even if they are bad for you.