All casino games and forms of gambling are risk vs reward. Or put another way, odds vs payout.
For roulette, a beginner will think betting most numbers gives them a better chance of winning (profiting).
An intermediate player will consider the odds vs payouts of each game.
A professional player will identify the weaknesses in each game and casino, to find "better than normal" odds. For example they might find be a blackjack player, but find a heavily biased roulette wheel. Or a roulette player might find weaknesses in baccarat for a particular casino.