Obviously we all have an opinion going into a trade and it's the opinion that price will go up or down in our favor.
I believe the danger is when the opinion becomes a strong opinion. I think we can all agree that there are lukewarm setups, good setups, and great setups. If you put on a trade based on a lukewarm setup, you're generally willing to bail at the first sign of trouble. Enter the trade on a good setup and you usually have a stop in mind at a price that invalidates the setup. But when you put on trade based on a GREAT setup (where 95% of the time in the past, X set up condition Y which led to Z), it's possible that you go in with such a strong opinion that when condition Y doesn't lead to Z, you might ditch your trading rules and, in fact, can be become totally blinded to the fact that if you'd simply switched sides when condition Y didn't lead to Z you'd have hit the home run you were hoping for.
