To become a good synchronized swimmer is required: stamina, strength, flexibility, agility, and that you are a good and fast swimmers. A good ear for music and rhythm is also a big plus. In a contest you push yourself to the absolute limit. You have X number of minutes (depending on age and discipline) to show off your skills! One can compare a synchronized swimmer with gymnasts or dancers, but in the water.
If you can get acquainted with how hard a program really is, one can draw similarities to other sports to understand. For example, you can compare it to swim 400 meters freestyle, or run 800 meters. Add to this that you can not show a trace of fatigue or lactic acid, you will always have a quiet and relaxed facial expression. Also, you have only limited access to air. There you have, roughly, how one feels during a program.
The sport draws heavily on swimming, but it is more varied and more fun. It requires, as in most other sports, and much hard training to get well. Synchronized swimming is not only fun to carry but also very beautiful to watch.