Define trust

Sometimes life tells us more than we can understand.
Sometimes understanding is not something you can have easily or assume people would have it for the things you've done or the way you've done things.
My grandma used to say that there is no use of being honest if you don't look honest.
Not important to feel like you're honest enough but that people see you as honest as your heart beats.
Hard to trust someone,hard to trust anyone when the impression is what it counts.
What would it take for me to be able to define trust?