This way if later the gambler makes a wrong decision and if he makes a wrong decision if he loses money then he will still lose part of his profit but in this case his capital will be safe.
What if you only get profit when you already have spent at least half of your capital and now your profit is not even double your original capital and the profit is quite too small to take the capital out and continue gambling?
This can only work if the profit is really high because I think most gamblers would most likely want to keep gambling with 2x the amount of their original capital for even bigger chance of winning bigger money.
Timing is everything.
Every responsible gambler must have a amount they risk on gamble, let's say they can only gamble two times in a week, maybe Wednesday and Friday, they must have a amount specifically for this two days, like $5 each, that's $10 per week for gambling. Now if they win like $50 on a Friday for example, this doesn't mean that they should use more than $5 on the coming Wednesday to gamble, a gambler has to be disciplined.
Whatever you win is yours, it has nothing to do with how much you should risk next, keep using the $5 on your Wednesdays and Fridays, it is going to look normal for you if you keep losing the $5 because you are able to afford the loss but when luck finds you, make sure you remove the whole amount on that day and wait for the next day.
When the next day comes make sure you keep risking that same $5, this strategy is what I consider the best one for responsible gamblers. I can't seem to find anything better than this.