There is a garden variety of arbitrage or quasi-arbitrage trades where you are a guaranteed winner if you do everything correctly. However, most people that have no losing months simply trade more frequently and their win rates are relatively low. An average HFT strategy has win rates of 51-55% and PnL/tradevalue of fraction of a tick. However, do that a thousand time a day and you would rarely have a losing day.As far as 100% win rate. No need to discuss that, because it's impossible to have a 100% win rate and make any type of consistent returns relative to your account size.