How did Galileo's success hurt his career?

Answer 1

It was his lack of success that hurt his career. He asserted that the Earth orbits round the Sun following the Copernican theory. The church authorities said that while this could be taught as a useful theory and model for predictions of the planets' positions, it was by no means the whole truth because no adequate evidence for it had been found.

The Copernican theory used circles and epicycles, like the earlier Ptolemaic theory, with the difference that the Sun was at the centre instead of the Earth. What caused the rift was the part where the Sun is assumed to be at the centre. Galileo maintained he had proof but that the cardinals were incapable of understanding it.

The curch responded by putting Galileo in court for heresy and asking for the proof, but Galileo could not produce proof.

In later centuries plenty of proof became available but in Galileo's time there was no proof, so in his own time he was proved wrong and this hurt his career and reputation.