Why dollar lost hurts more than a dollar won feels good? Bernoulli's 1738 utility theory explains risk aversion well. Basically, marginal utility from every next dollar earned shrinks as you get richer and widens as you get poorer. In other words, you value most what you've already lost. When you lose $1,000 on $10,000 account, it hurts more than the joy of $1,000 profit on the same account. It's critical for trend systems, which are most profitable. With many small losses and few large wins, the wins have to be bigger than the losses. To make most money, search for asymmetric payoffs. Ideally 3:1.