I never truly acknowledged the importance of this sentence until today. My first trade today which was at the moment was my biggest loss and it was a setup I had never traded before. After this I began letting my emotions take control and kept forcing trades that I had no idea why I was in. I was essentially gambling. Overall, on the day I finished down 1.02k my biggest losing day, this day completely erased last week's gains and now I'm negative on the year.  I promise now to myself to only trade setups I know and that I'm comfortable with.