there's a thing

There's a thing. I don't know the name of it.

Let me try to describe to you.

When I see it, it is for sure.
When I not see it, a feeling of betrayal gnawed at the heart.
It is something people know by the heart.
People were met without it sometimes.
When that happened, people are usually disappointed, upset, and mad.
Because it was usually given in advance.

what is it?