Capitalism focuses on rewarding those who can use the resources available to them to the greatest advantage. It relies on the ideas of social Darwinism, free from the influence of social agenda, to select for the most fit approach. While there are different flavors of Capitalism, they share a common focus around supply and demand. The producer who most effectively identifies and supplies demand is most successful.
Capitalism's greatest weakness is a tendency for the rich to get richer. Once an advantage is gained, the leverage can be difficult for any individual to overcome. A combination of unionized opposition to the lead player and increased leverage from technical advancement help to keep this weakness in check.
Socialism, by contrast, tends to encourage adherence to a socio-political ideal. Ideals are often brittle and difficult to adapt to changing conditions. Centralized authorities have little resistance to corruption, and slowly drift back towards the benefit of the powerful few.
Socialist structures tend to have monopolistic organizations with little or no incetive to innovate. Capitalism, on the other hand, experiences disruptive industry innovation as new companies compete with their predecessors.
Yes, capitalism rightly harnesses individual desires, because a person benefits from their willingness to work hard. People will always be self-interested. That there is a way to translate those self-interests into something that benefits all of society is a positive thing. The trickle down effect also helps others benefit from the wealth in society.