We likely ask ourselves that same question on occasion as adults.
The answer to that is when the tools are given to us to see that our actions are what delivered the outcome. We learn when we know what it was we did wrong and shown how to do it correctly.
This is an example of this. You spill your milk. Your mother says "Be careful" and then proceeds to clean up the mess. You spilled your milk again. "When will you learn?" is asked. Once again, she cleans up the mess. How about the first time we spill the milk we are told that our actions were careless, we need to make sure the milk is in front of us and not by our elbow. Follow that up with cleaning up our own mess?
Mothers everywhere are thinking "But its a kid! They can't clean up milk properly." Teach them. Give them the tools and the consequences. You can do a thorough job of it later. It is the lesson we need here.
We can easily relate this blueprint of learning to ourselves. We will always make mistakes. When we see that we are making the same ones over and over is the time to examine where the mistake starts, what we didn't do to change the outcome and LEARN what it is we need to do the next time the situation or one like it occurs.
I often wondered why people think they can "fix" something they have never been given the tools to fix. When our car doesn't start, we don't expect that we can open the hood and figure out whats wrong and fix it. (Unless, you know, you are a mechanic). Why in the world do we think when our marriage is in trouble, our self worth is lacking or we keep choosing people in our world that don't serve us - that we think "I can fix this on my own."?
It takes strength to ask for help. Suffering doesn't make us stronger, it wears us down.
When will we learn? When we open ourselves up to. That's when.