What made Copernicus question the Geocentric Theory?

If ever Copernicus did question the Geocentric Theory, why did he? Did he think that there was something wrong with Ptolemy's proposition or did he just find Ptolemy's proposition too complicated to comprehend? Did he find evidences disproving the Geocentric Theory or did he just think that there must be some other way? What made him think that the Geocentric Theory was somehow wrong?