Is that their fault?

Very good question because i do not have the answer. Has my trust been broken? No.
But i believe people are bound to disappoint you, because if they don't they won't be human after all.
I don't even trust myself completely, how will i then trust someone else.
Its just like you said

Trust is a complex system that is full of a wide range of variables that are very hard to predict when they influence upon each other and as contexts and circumstances change.

Situations and circumstances will always change and most of our decisions are based on these factors. So when giving your trust, take into cognizance that there is a possibility of it being broken. That way you save yourself a lot of heartache.
That said, I'll wait for you to throw might light on this issue of trust.