The closest people will know that you gamble no matter how it will be hidden they must know it, now imagine gambling is almost everyone knows even though they never play for example.
There will be more people covering up their shame than saying that they are addicted, which is clear that they know how to do it, they just don't explain that they also have the same problem.
When it comes to physical habit, then almost everyone can see it, especially the people around you because the world is small and once someone sees you playing, that's it for you, you cannot take it back and the whole community will know about it and you on the other hand, no matter how careful you are, when you caught red-handed like that, it's all over and your secret is done. No one has ever been good at keeping it a secret unless you are playing in another city but once you get addicted, the symptoms will show and they will get curious to know the cause of it and eventually find it out.