I've heard people discuss trust. Even on radio. And sometimes, when I listen on their discussions I wonder if they are being sincere and human. They talk about principles and rules of deciding if someone can be trusted or not. They relate their numerous experiences, involving a breach of trust.
I wonder if they have ever asked themselves this question: "Have I never suddenly changed my mind before?"
The truth is that trusting someone is an act of faith. You are taking a big leap. Everyone of us has changed his mind suddenly before. And we all of have our very convincing reasons for it. But regardless of reason, trust is dependent on staying true to your promise. Which is beyond any human. There will be situations, life threatening situations, that will make us instantly abandon a promise.
It's true that some people are experts at encountering circumstances that make them renege on their promises. The weather can be enough reason for them to breach a trust. Yet, there is none of us who can say he's 100% sure of fulfilling whatever he promises. Even the bible admonishes us to say, "If God wills, I will do..." Being 100% sure of what he would do was the Rich man's main fault, who's barn yielded much increase. He forgot that he needed to be alive to do them and that his very life was not his.