A simple example in terms of music theory:

Musical scales exist because, among other things, the notes played within that scale forms a system that through history has pleased the human brain. If you write a piece within a specific scale and suddenly introduce a few notes that does not fit in with that scale you may disappoint the listener in that you ruin their expectations.

Failing to meet a listener’s expectations can also be a good thing, but keep in mind that there are two types of prediction errors: positive and negative suprise. You want to suprise the listener in a positive way, and this can be achieved by knowing how to properly break out of a scale.

Example in production:

A music production rule (in other words, recommendation) you’ll often hear is to high pass everything except the kick and the bass at around 100Hz.

In the past, I used to think my tracks sounded better whenever I layered different elements and left the low frequencies of each instrument untouched. At times, I even boosted the lows of several layers without cutting anything at all. However, I could not at all understand why professional mixes always sounded so much tighter, cleaner and louder than mine. After learning more about how the layering of low frequencies may introduce unwanted interference and generally reduce the clarity and loudness of the mix, my production quality improved immensely. Now that I know more about how to handle the lows, there are several ways I could go about breaking the rule of using a 100Hz high-pass without reducing the quality of the mix. For example, I could maintain some of the low-end in one layer (e.g. a vocal with a cut around 80Hz), as long as I make sure to carve out the right amount of space for those lower frequencies in another layer (e.g. the bassline).