Happened with me last year on the roulette table. I had around 1 btc on the table, and was betting small (0.05-0.1 btc) mostly on black/red and the rows. Mistakenly, I dropped 0.1 BTC on a number just seconds before the countdown closed, and I got lucky that it landed on the number. Most excited I have ever been on a roulette table. It was an easy almost 3.5 btc of profit off that mistake.
That is how it works most of the time when you make a mistake but then it ends up winning for you.
Just when you least expect it. It always seems to happen this way.