Sometimes having a lucky win can be very scary, you know how slim the chances are of winning especially when it's a big odd, for some people winning from such might be a trigger to continue gambling while others might decide to take a break. As for me whenever I win I always slow it down for a while because I know that there's a high chance of losing everything my profit if I'm not careful
Instead of scary why not use the phrase over exciting. This mostly happens to beginner's in gambling, especially when they have their first win/big wins. The excitement kicks in, with no one to guide them, they will be triggered to start betting impulsively. From my experience, wining often in gambling, gives you a much higher chance of gambling again, because you are on profit so you have the mentality that you are gambling with the profit you make not the capital thus you still have more money in your bankroll.