This is what Jesse Livermore had to say:
You may remember the story I told you about that time when I was short thirty-five hundred Sugar in the Cosmopolitan and I had a hunch something was wrong and I'd better close the trade? Well, I have often had that curious feeling. As a rule, I yield to it. But at times I have pooh-poohed the idea and have told myself that it was simply asinine to follow any of these sudden blind impulses to reverse my position. I have ascribed my hunch to a state of nerves resulting from too many cigars or insufficient sleep or a torpid liver or something of that kind. When I have argued myself into disregarding my impulse and have stood pat I have always had cause to regret it. A dozen instances occur to me when I did not sell as per hunch, and the next day I'd go downtown and the market would be strong, or perhaps even advance, and I'd tell myself how silly it would have been to obey the blind impulse to sell. But on the following day there would be a pretty bad drop. Something had broken loose somewhere and I'd have made money by not being so wise and logical. The reason plainly was not physiological but psychological.