Just Because

Just because something has lasted a long time people assume it must be good.

"You've been married 50 years? You must have such a good marriage!"

No, not necessarily. Maybe it was really bad. Maybe they stayed together out of fear, obligation, expectations, laziness. Maybe it was too much trouble to go through a divorce, tell the kids, give up the life they were accustomed to, figure out who kept (or was stuck with) the dog.