You are always going to end up with gains at some point if you play long enough, all is to know when you are on a "lucky streak" and you have more chances to loose than win in the number of rolls you can play compared to what you gained so far.
Simply "quit while you're ahead"? Yes. That would be a smart move for any gambler. However it's incorrect that you will always end up with gains. Due to house edge and not having unlimited funds it's more likely that you will end up with losses.
If you want to play 1000 times and you're just ahead of 2% you can still have chances to do better, if you just did x3 after 2 rolls, it's very unlikely you're going to beat that unless you want to play a very long time
