Playing the game, changes the game
. This means that if you take a break to use the bathroom and your number hits while you're away... that you may not have won had you stayed to play.
Had you stayed...the dealer may have taken more time before spinning the ball. If there's more time before you bet, then more of the wheel will have spun by before the dealer launched the ball. This means the physical alignment of the ball on the track and the wheel speed will likely have been different enough to have generated a completely different outcome. If you had stayed to play, then the chance of you winning on that winning number, straight up, was still only 1/38.
If you want to go to a deeper level, then you could theoretically argue that quantum mechanics even proves that simply observing an event is enough to change it. However...it sounds absurd mentioning quantum mechanics in a roulette thread. Now I will have to go and ridicule myself for even having mentioned it.
If you had a time machine, and you could travel to the past, then you'd still likely change the outcome because you were at the table instead of in the bathroom...again changing the playing conditions and observing the event.
Everyone that plays must overcome the "would of bet that number but missed it" syndrome. This leads people into betting more and more numbers at every spin, and doing silly stuff like hedging the outside bets by betting on the zeros. Let go, use logic, and don't get upset if "your numbers" hit when you're not on them.
Don't bet on so many numbers. Overtime you're more likely to still be a winner if you bet on fewer numbers. In order to bet on fewer numbers you have to beat the syndrome above.