Music is often about creating "tension" (and release).
For example, 12-bar blues are like this (where each letters represents a bar)
A-A-A-A D-D-A-A E-D-A-E ...and back to the start. For hours.
Throughout the 12 bars, the tension gradually builds.
If you do it right then the tension has built so much that by that final bar ('the turn around') you can throw everything you've got at the instrument, dogs, chickens, bottles, a whole piano. And then we're back on the flat again, stepping through the A's.