In my late teens and early 20's I had a lot of book & observation based business information contained in my brain. The most jarring thing about running a real business early on was all the ... bullshit. Most of which is unavoidable. The myriad of issues and red tape, that have nothing to directly do with creating or selling or product or marketing or managing.

The best thing to come out of those early experiences in my opinion, is the automation you properly build up that makes it possible to fly a lot faster through it all with each iteration. That part of experience is priceless. I waste a lot less time now, and know a lot better what to focus on.

I don't think any business school can teach you the kind of fast reflex adaption you acquire with experience. No two scenarios are ever the same, but with enough experience you'll find a lot of cross over similarities, things you learned over there that apply well over here. It becomes personal data that you can call upon instantly, bend, manipulate, adjust to solve new problems fast.

Data from experience is more easily available for manipulation to new problems than mentally distant 'book based' knowledge.