I always tell this story about working with sales at a job where I worked in tech support. Sales would call me up and ask why I hadn't talked to their client about their very important ticket.
I would tell them:
"I have 5 P1 tickets, 8 P2 tickets, and dozens of P3 tickets. Your ticket is a P3 ticket."
They would ask that I change it to a P1. I would. Then they would call me an hour later asking me about the ticket and I would tell them:
That's when they understand that they have to start fighting their peers and talking with the big boss to get their P1 ticket moved in front of the other P1 tickets.
Yup, but it gets them out of my hair, and they understand the support guy isn't in a position to wave a magic wand for them. If sales guy wins his fight with the folks in charge and I get time / resources to work on his thing, fine with me.
At Symbian defects were classified from P1-P4, with the inevitable shit-fights about adding magic runes to the title so everyone knows that your P1 is more important than theirs.
The day came when, after prolonged hand wringing and with stern observations about great power and great responsibility, the priority could be set to P0. But like any bunch of junkies we came off this new high all too quickly and the P-1 classification arrived, the showstopper of showstoppers.
In hindsight what I most regret is that we stuck with an integer field; we were denied the expressive power of fractionally critical issues.
So? If they succeed (big if), then that ticket is your new priority. Maybe even for good reason, maybe not. But usually you don’t care that much which one you work on first, do you?
Good for them for at least understanding at that point. The typical response is to say "I get that, I really do—can you move this one to the front of the line for me?" and then maybe a vague threat like "I can talk to your manager if it would help".
In my experience, when it's other people deciding the priority of your tasks (usually your boss), the distribution is 150 P1 tickets, 3 P2 tickets and 1 P3.
This is when the underrated skill of saying NO pays off massive dividends. One long-term client once told me the thing he appreciated the most, compared to most other consultants, was that I wasn't afraid of pushing back on his requests and saying no (within reason). Probably the most valuable feedback I have ever received.
When I worked support, they didn't even have a priority system (it was C2B, so there weren't necessarily enterprise customers. That did come later, with LiveChat and all it's joys). Instead, we had a 24hr expected turnaround and harder tickets would naturally filter to the top. Tickets that had reached near that point had a higher weight, which went towards your metrics/"leaderboard status". To dissuade gaming of the system, ongoing replies were assigned to an agent (you wouldn't give a half-assed reply and then hope for someone else to clean it up) and were exempted from the bonuses (so were one standard ["fresh"] ticket each).
Obviously, there was some oversight from managers, but overall it worked pretty well.
I would tell them:
"I have 5 P1 tickets, 8 P2 tickets, and dozens of P3 tickets. Your ticket is a P3 ticket."
They would ask that I change it to a P1. I would. Then they would call me an hour later asking me about the ticket and I would tell them:
"I have 6 P1 tickets."
That's when they'd understand ;)