[obenn]

The 0 does not count as a lower number. There at 18 numbers in both the groups 1-18 and 19-36. Each of these give a 18/37 chance of winning, which is lower than 50% and therefore loses in the long run when the money is being doubled on a win.

[potatote]

Ah...I see. I am not much of a gambler either, so this is a very useful piece to know why Roulette gambling, in the long run, turns negative for the gambler. Thank you.