Answer:
If an organism has a beneficial trait, they have a higher chance of survival, and if they can survive they can reproduce too.
Example: Speckled moths camouflage with the bark of trees and are not easily seen by predators. Black moths do not camouflage with the bark of trees and are easily seen by predators, therefore the black moths are eaten. Because the black moths have been eaten they cannot reproduce and pass on the trait for black wings to their offspring, but the speckled moths are able to reproduce because they survived and are able to pass on the speckled wing trait to their offspring.