"G" is for..................

Good swimmers are often drowned.

This proverb warns of overconfidence (being too confident).
I can think of many times when I let my confidence in my ability to become too great, and as a result, I failed badly.

I will use sports as an example:

I am decent at basketball. Once, I was having a great game and then I let myself get overly confident. I started joking to the other player, "You can't score on me". But, then the game changed. I started missing shots. I couldn't block shots. My overconfidence had overshadowed (become greater than) my ability, and I could no longer focus on the game.

That is what this proverb means to me:

Beware of letting your competence (ability) lead you into overconfidence.