What specific, erratic planetary behavior forced the geocentric model to adopt complex additions like epicycles?

Answer

Retrograde motion

Planets like Mars, Jupiter, and Saturn periodically appeared to slow down and move backward for a time, a phenomenon known as retrograde motion, which the model struggled to explain simply.

What specific, erratic planetary behavior forced the geocentric model to adopt complex additions like epicycles?
modelastronomystrengthWeaknessgeocentric