I disagree with the above statement because I sit next to such a scalper and he consistently wins but he's very disciplined (except for his attitude since he is always swearing and its annoying since I have to sit next to him - I just put on my ipod)
One tick scalpers, more so than other traders (i believe), require a lot more discipline than other traders because as soon as they see the market (or similar market like the Gilts if one is trading the Bunds) go any way slightly against them, they will be ready to scratch the trade (even if it goes bid, offer straight away - then the swearing starts) or take that 1 tick loss max max max, a 2 tick loss is a disaster. A lazy scalper will only take 1 tick profit (never run his winners) and take the mother of all losses as slippage happens. Therefore, it requires such an intense amount of concentration that I am not sure I could do it for more than 4 hours a day, especially as US opens in the afternoon but then in more active markets I think one should be looking for 2 tick scalping opportunities.
Therefore, a good scalper will probably take 1 tick profit from 60% of trades, scratch 30%, 2 tick loss 5% and 3 tick loss 5% of the times. Over time that adds up.