Let's imagine you have 100 € invested in the stock market.
If you lose 50%, you have 50 € left.
To return to 100 € from 50 €, you need to gain 100%, because 50 € × 2 = 100 €.
So:
A loss of 50% requires a gain of 100% to compensate.
A loss of 20% requires a gain of 25% to return to the starting point.
The greater the loss, the higher the percentage needed to return to break-even.