A seemingly simple quote from Ron Swanson, of the TV show Parks and Recreation, I think its often easy to think you can do everything.
Sometimes it happens slowly at work, you start with a plan and more tasks come up with varying priorities, each seems to be more important than the next one. Are you expecting to give 100% of your effort on each of those tasks and get everything done on time?
I think the most important thing to consider when getting multiple competing priorities competing for your time is to understand what is being asked of you and how it ranks amongst the other work you have on deck.
On my team lately there have been many disruptions to our primary feature delivery for other important work and our resolve is to ask the requester to provide a priority and to know what doing this work will do to other priorities.
To take it a step further, these discussions should be happening at a program level - trading A for B will delay A by 2 weeks - and have sign off from all parties impacted by the decisions.
We’ve all tried to deliver everything being asked and quickly learned we either burn out from working too many hours and taking on many change requests, or we flat out fail at delivering anything. So when it comes to competing priorities, go simple - Don’t half-ass two things, whole-ass one thing.