You can actually only ever have one priority. Everything else comes second!
Up until as recently as the beginning of the last century, priority was a singular word. It didn’t have a plural. There could be only one (to take a quote from The Highlander!). The etymology of the word suggests that it means “coming first compared to another thing; the state of being prior.” (http://www.finedictionary.com/priority.html) There can literally only be one thing that comes first.
If you look at the Google N-Gram search for the plural vs the singular you can see that the plural was not used prior to the 20th century at all and only really became popular shortly after management consultancy took off in the early half of the century.
It seems that having multiple priorities was a symptom of trying to be more productive, get more done and make things more efficient in the industrial economy. But if you think about it, it’s not really possible to have more than one priority. Firstly, you can only focus and work on one at a time anyway. And also, what happens when two of your five priorities are at odds with each other? If they are pulling in different directions? What happens when resources are required in two different places at once? What decision will you make? Which priority, or team, or action will get the attention?
With one priority it’s easy. The priority wins, with eight, you have to decide. And what you decide, that’s the real priority!