Basically, the more often people bet, the greater the chance of winning and also the increase in the number of losse. Someone who would be said to be a professional gambler is someone who relies heavily on his skill and expertise in gambling, has a mental and style. But all of that will still depend on luck. I just assume that all gambler who are able to control their emotion and manage their finance in gambling will be called professional gambler.
If we are talking specifically about gambling and not about gambling where there is an element of skill, then the picture is exactly the opposite. It is quite easy to win at a distance of 10 bets, at a distance of 100 bets it is more difficult, at a distance of 1000+ bets it is almost unrealistic. The larger the number of bets, the closer to theoretical results (and the casino always wins on them).