Money is not exactly 100% necessary for success in life but is probably very correlated with it especially when considering having enough money is important for food, shelter, water as the basics. To keep it short though, the culture of western society promotes an environment that is conducive to having more wealth (for several reasons both unknown and known). More wealth aids in attracting a mate, regulating the neurotransmitters in your brain, and providing you with more experiences to enhance your understanding of the world. Exceptions to the rule: Ghandi, Galileo, Jesus, MLK. Basically the other option is fame (correlated with money), civil activism, science, or religion and money frequently flirts in these arenas.