Ear Training doesn't mean doing push-ups with your ears. It means learning how to recognize musical notes in relation to other musical notes by sound only, without looking at your instrument.

This ability and skill is very important for a musician, just like it is important to hear and recognize words in a regular conversational language.

In any language we start learning how to hear and recognize words pretty much from birth.

In the language of music we have specific ways to train our perception and recognition of musical sounds.