The principle is to recover losses without too much risk.
This plan will add one unit after one loss. If you are betting 10 units, then the next bet (only after a losing bet) would be 20 units.
After one win the stake will stay the same if the last stake is the same as the starting stake, or will decrease by the % if the last stake was bigger than the start stake.
In this case 20% would reduce the stake by 1/5 every bet until equal to the start stake.
Bet
Stake
Result
1
10
loss
2
20
win
3
18
win
4
16
win
5
14
win
6
12
win
7
10
win
8
10
win
If you want to use this plan it's advisable that you have a bank with 100 times the 1st stake to be comfortable. I.e. A stake of 10 would need a bank of 1000.