Hello!!does any of you know what does "at mastery" "mean??ok, i'll give ya the context : "it's not surprising?

Mastery is the act of trying to master a function or idea. Like trying to lear to read, or use the potty etc in the context you have used it. The frustration that children will experience trying to master, say walking, can drive them to tantrums with the frustration of not being able to master the act.