> It also ignores another big factor if psychology, humans are a lot more afraid of losing what they have than gaining anything.
Rightly, I think. The marginal utility of the next dollar is higher when you have fewer dollars. (I think of it as roughly a 1/x curve, but I have no solid data for this.) This means that, if I bet 50% of my available money on a 50/50 chance, I will lose more utility with a loss than I will gain with a win.
But the more I have, the flatter the curve out where I am. So the richer I am, the more I can make that 50/50 bet, not just because I can take the loss better, but also because in terms of my personal utility, the rewards and losses are more evenly balanced.
Also note that if you have a 20% loss, it takes a 25% gain (on what you have left) to bring you back to even.