the most important mistake in trading that we should avoid

Dear Trader,

What do you think which is the most important mistake in trading that we should avoid among these.

1. Trading with money you can't afford to lose
2. The need to be "certain"
3. Words that will kill you! HOPE---WISH---PRAY
4. Not Acting on your plan
5. Not knowing how to get out of a losing trade
6. Having an ego
7. Falling in love with a sector or script

Regards
Anand