Do you mean 2% for stop loss ? With high volatilitas of crypto, i think that too small percentace in crypto trading, for the better use minimum 3% to 5% for stop loss and take profit minimum 10%. Stop loss 2% can be better to use in stocks trading that has lower volatility than crypto.
You are getting yourself confused, it is not about earning 2% on each trade, it is about not entering a position with more than 2% of the total capital you have. I believe that should be explanatory enough for anyone. This would always make it easy for you to make trades without having to worry about how much impact it would have on your general holding as the case may be.
It is a form of risk management or money management, however you want to see it. If you go all in on a single trade, you set yourself on a higher risk and even when other opportunities arrive to make other trades in some other potential markets, you become incapacitated to get in.