Risk-reward (R:R) is the mathematical backbone of strategy design. If you risk 20 pips to make 40 pips, you have a 1:2 ratio. If you risk 20 to make 10, that is 1:0.5. At 1:2 you can be right only 40% of the time and still be profitable before costs — at 1:0.5 you need to be right over 70% of the time.
There is no universally "correct" R:R. Scalpers often run 1:1 or worse because they get a high hit rate from short-horizon mean reversion. Swing traders often run 1:3 or higher because they catch large trending moves less often. The key is matching R:R to the realistic win rate of the setup.