It's important but I wouldn't say it's the MOST important thing. I think tolerance is more important than discipline.

I would argue that it's the most important thing to learn because most of the truly important stuff is already natural to children. Discipline is not intuitive to learn. Creativity, tolerance, and curiosity are all more important than discipline. But creativity is so baked into us that we're destructive to our environment as children. Curiosity is so baked into us that small children seem hell bent on getting themselves killed. And tolerance isn't a thing we "learn". Intolerance is the thing that we learn, and later as a adults hopefully unlearn. Children are born innocent. Don't raise the kid to be intolerant in the first place and they won't be. Discipline, however, comes with time, experience, and a whole lot of unpleasant work. It's important, yet almost unnatural. edit: Actually, I suppose kindness and particularly NOT being mean is also really important, probably more important than discipline. Being kind is intuitive to a kid, but sadly so is being mean. So I suppose I'm not PERFECTLY "For". But I do maintain that discipline is severely lacking, and underestimated in society.

What a lot of people dont realise is that, this isnt about punishment discipline. This is mental discipline, and it is one of THE most important things a child can learn, as it will drive them on to a better future and build something of their lives.