My experience, with a wide variety of generally older friends & associates & such -

If they're talking about an occasional visit to the casino, people will be up front about the fact that they walked into the place with $X in their pocket, and walked out with $Y. Almost always, $X > $Y.

If they're talking about stocks they've bought, people will be incredibly selective, and describe only some of their greatest successes. They could lose money in a rising market, and you'd have to carefully question them to even realize that fact.