With back-testing you can get some idea what is the probability of a winning trade versus a loosing one.
Loosing trades, especially, happening in a row eat up the money of the trader. This is why people need money management.
However, counting the probability of loosing trades is very easy. It is 50%.
Price moves up or down. 50-50% chance of loosing or winning no matter if it is short trade or a long trade.
I am not sure that even with backtesting you get a better answer than 50-50. Why? It is called backtesting drawdown. Backtested strategies tend to get weaker as time goes forward.