Chaps_x,
The core difference between trading a
demo account and real account is the psychological factor.
In demo account, you've got nothing to lose. Are you risking something there? Will you feel very scared when the market is approaching your stop loss point? I believe not.
But with real account, you've got something to put into risk. You can lose your money. It is a painful experience to wait for the market to move in accord to your expectations.
You tested your system using demo account or maybe paper trading. I've been there before, and I don't feel significant pain when my stop was hit. But when I put them into real account, I felt so awful when my stops were hit.
If you play flight simulators on computers or video games machines, you won't feel scared when your plane is about to crash. But what if you're on real plane? How would you feel?
In short, in demos, emotion/psychology is not included.
Cheers!