Grown-up phone calls
When we are younger we have a thing that if someone says they will call back, it usually means that they will call back within the hour, not a few days later. When this happens, the younger version of us would get very annoyed and mad, refusing to talk to that person forever.
But this is a very immature way of looking at things, in reality, people just get busy and it is nothing to take personally. That is why adults usually just do not care if someone never calls them back or does it days later. What is there to say, life happens.