Was it greed or simply lack of awareness, but it was the wrong idea of Bellerophontes. Furious because Bellerophontes even dared to think to come to the heights of the Olympus, Zeus sent a gadfly towards the flying guest. Pegasus was stung and disturbed and Bellerophontes lost his balance and fell on the ground.
Athena, as it’s said, spared his life softening the ground for the fall, but until the end of his life, the crippled and lonely Bellerophontes was hiking around looking for his precious Pegasus. Of course, he never found him. Pegasus continued to live on Mt Olympus, where Zeus welcomed him and kept him as his favorite and most important steed. The myth says that Pegasus was loyal to Zeus until his last day.