No need to read all of Jesse Livermore: The Greatest Trader Who Ever Lived, but here is a 100+ year old quote that still applies today:
“The successful trader has to fight these two deep-seated instincts. He has to reverse what you might call his natural impulses. Instead of hoping he must fear; instead of fearing he must hope….It is absolutely wrong to gamble in stocks the way the average man does.”
via Eddy Elfenbein