I recently posted following in a forum:

it sounds like gambling, but Monday dollar will be down. I think.

Here what I got as a responce, I believe he is right:

I'll just make a quick comment on what you said above based on my own personal experience. It is when "I think" that I get myself into trouble. What I mean, is if have a preconceived thought on which way the market or a stock is headed, then I am inviting emotions to play havoc with my trade. IMO, it is best not to have a preconceived notion about something as the market is never wrong, only you are.
Emotions set in and most of us don't have control of our emotions the way the professionals do and that is why most traders lose money.