It's taken me a long time to get that into my head. Sometimes, it happens to quick, and you look at that 8% and think... "Hmmmm I just got that in 30 minutes, maybe I can get 15% if it just ...." and then moments later you're down -4%. A lot of psychology involved. Which is why I banter so much about it. I have to keep knocking it into my head. See profit - take profit.
These thoughts are just mine, not right, not wrong, just thoughts. Invest in what you believe in, not what I believe in. Do your research, and invest in the facts.