One of my pet hates is when someone refers to humans as the ultimate success of evolution. And this is why.
The most successful forms of life are the ones that are superbly adapted to their ecological niches, and never have to change much. Many bacteria that live on Earth today are essentially identical to their ancestors that were around when the world was young, three billion years ago. They are the great survivors, the true successes of evolution.
But when individuals are finding it tough going in the competition for food and other resources, they have to, literally, find pastures new. This only works if the new pastures are not already occupied. The reason life in the sea doesn’t move on to the land today is that there is plenty of land-based life around already, and any hypothetical proto-amphibian that flopped out of the water would soon get eaten.
Long ago, however, the most successful fish stayed as fish, and their descendants are still fish today. It was the fish that weren’t doing too well in the seas that were pushed to the margins, the tidal mudflats where they developed into amphibians, moving in
land to eat the insects which had followed the plants out of the shallow seas. Similarly, it was the least successful amphibians that had to move on, adapting completely to dry land and becoming reptiles, and so on. We are descended from a long line of creatures that were not very good at their roles, and had to adapt or die — a long line of near failures, in evolutionary terms (not complete failures; those species left no descendants at all).
The ultimate success of evolution is to survive and reproduce; nobody has done it better than the archaebacteria.