the lesson that investing comes with risk and that losses are an inevitable part of the game. it is one thing to say you are a risk taker and buy a spec stock, and another thing to fully accept that risk, which ultimately means to take losses and move on.
the lesson that your own mental makeup is largely what determines your success or failure. only you decide when to buy, hold or sell. to a large extent, YOU create your profit or loss. its easy to buy, but its the selling that is the tricky part. most of us learn this after a few bad runs.
the lesson that no matter how much of a sure thing something is, or how much research you can do, the market can, and often does move against you. over time, you learn to stay objective throughout a trade (lets face it, most prop investors are traders with their interest-only loans)
from the conversations i hear these days - friends, workmates, in coffee shops - i propose that many first time and/or recent investors that have jumped on this bus in the last 5 years are simply not equipped to deal with the rules of the game changing on them. i believe they are mentally not ready (and hence able) to act on scenarios other than the sure thing that the seminar/friends/tv told them: prices always go up.
you might have mastered the mental, kingy. i certainly haven't, but i'm making progress through my small stock trades. the key to successful investing is mastering your own state of mind and that can't just be taught. the above comments may not be anything new to those on this board that have a keen interest in trading/investment/speculation but my point is that most prop investors don't actually have a keen interest in investing and haven't taken the time to learn. they just want the quick and easy path to prosperity. i know plenty that don't even know what the term leverage means!
they have lined up and taken their seat. their blindfold is on, all their chips are in and their rollercoaster ride is just stalling at the top. but this isn't dreamworld and the ride will be a lot longer than 40 seconds.