Spot on.
Day trading is a loser game.
How come some people still do it then?
If you're not too greedy, and you're satisfied with profits of about 10% on a trade, and you don't panic sell or buy, it's not that hard not to lose money really.
The trouble is that the caveats you listed are some of the hardest things to conquer for many new traders. Even after time it's hard to shake off a habit. Aside from the discipline that you mentioned, it's all about believing in your trade.
I'm a terrible day trader, I am ultra bear short-term e.g. the belief that someone will dump hard and trigger something bigger when I buy in. It can take quite a while to recover, as I have found out with Peercoin of late.