Trust is something we can't trust unless one knows own self. When one knows how he or she can (capability) put their words into the exact action, execution and effort towards a task or gave words to the one we got bonded so.
All the thing is one is eligible to be trusted only and only when they put the same in efforts and their words. Then their is only a Plan A nor other any plan.
Its like how much a machine is efficient and reliable in its work. Output/input * 100 so same goes for a human.
Well trust is more complicated.