That's true, many people under impression that they will mostly win in the beginning and only start losing after that but that is not correct. One time I got more than 10 continuous losses in dice, not in the roulette game. I agree with you that whether you play for long or short there is no guarantee.
Well it would be 50% but if you add provably fair on the casinos, the advantage they have, it would seem like less than 5% of the advantage of the casino is against the player. And the more you play the more larger that percentage is and thats what I think is going on if you play in the long run.