In water, penguins are in their element. They spent most of their lifetime in the ocean. The body of penguins shows some adaptions for a life in water: strong flippers for swimming, a spiky bill for foraging and a streamlined body shape for less resistance while swimming. Moreover, their coloration functions as camouflage. If a predator looks at a penguin from above, the predator would not be able to differentiate the black back of a penguin and the dark background of the deep ocean. The white front of a penguin resembles the light water surface, so a predator which is beneath the penguin cannot recognize it when looking up.
On land, these adaptions do not help penguins or protect them from predators. They are much more clumsy on land and especially young chicks fall victim to predators like raptors because chicks are weak and unexperienced.
Particularly the great food supply lures penguins into the ocean. Here they can find diet like fish, squid, crabs and krill which is especially favored in Antarctic regions.
Nevertheless, penguins have to enter the land regularly because they lay eggs like all other birds and they have to rear their chicks.