This came out of a WhatsApp group flame war, but it’s true – priorities are a zero sum game. Whenever you prioritise something, it comes at the cost of something that you have deprioritised.
If you say that “A is a priority in addition to B”, you are being dishonest, for in your book you can either prioritise A, or you can prioritise B. If you want to increase the priority of B, it necessarily comes at the cost of A.
It doesn’t matter what you are talking about here. It could be national economic policy. It could be your company’s vision statement. It could be about how you choose to spend your time. It could be how a computer operating system works. Priorities are necessarily an ordered list, and there is always something that is of the highest priority.
This, however, doesn’t mean that priorities cannot change. A good system is one in which priorities are dynamic, and change according to the needs of the situation. A good example of changing priorities is the “shortest remaining time job first” paradigm that operating systems use.