Old short story where a man crash lands on an alien planet with hostile environment. He thinks he is gradually changing the environment to suit him, but actually he is being changed to adapt to the planet
"Enchanted Village" by A. E. van Vogt.
Astronaut is trained in the importance of adaptation for survival.
He crash lands on Mars and finds an alien village. There are no aliens but the buildings are living creatures.
Astronaut tries to get the buildings to adapt so they can feed him and supply water. He fails.
But he does not realize that he himself is adapting.