Sometimes, as a pilot, we have those little brain lapses too. One person looks at the person next to them and says, what did we just get cleared for? In those situations, standard procedure is to just ask the controller to make sure instead of trying to figure it out ourselves.
Additionally, different countries have different rules about altitude restrictions and again, sometimes we have those little brain lockups that make it easier to just ask for a little reminder than cause a major issue.
I mean, I've heard. Wouldn't ever have happened to me.....
