I would agree with this, you (as the parent) know its a mistake and you want them not to suffer for something they could avoid but you can't teach what the mistake does.

That said, I am a big fan of having your kids make their mistakes and failures early and often. It is so easy to help your child avoid failing at some task, and yet doing so robs them of the value of not failing. Or more succinctly Success is measured in failures. If you try to do something and fail at it several times and then succeed, that success is that much sweeter than trying something and exceeding without ever failing. Thus success without failure is hollow.

So like the example of watching and encouraging your kid to walk, responding to failure with compassion and support is just as important.