I think you already mentioned the answer you're looking for. Playing roulette is all about guessing what number will appear to win, so it is all about luck. Roulette is like playing lotto, there's a lot of possibilities, a lot of sequence on which number will be the key of winning. The more numbers of choices you have, the lesser the price you'll get but the odds of winning is higher compare to betting only single number on which the payout is huge but the chances of winning is very low.