It’s important to remember that someone else’s lack of planning is not always your emergency.  Even if their situation really is dire, and even if it directly impact’s you, your best course of action may be to put that item down as “next” on your list, rather than dropping everything to deal with this new issue.

It takes a significant amount of time to switch your brain to a new context. See Umich study. Every time you change tasks, you leave your prior task in an unfinished state, figure out what has to happen with the new task and then get started on that.  If new tasks keep landing in your lap sooner than you can get the old one done, you have to switch contexts more than once per task.  If your tasks change often enough that the context switching takes longer than the time spent doing your task, you are thrashing.

The longer you spend working productively on any task, the more effective you become.  When you switch from one task to another before the first is done, you have to add the time it takes to familiarize yourself with the new project to the time it takes to finish both tasks.

We each have several lists of things which needs to be done.  We have a long list of things which need to be done some time when you get a chance, like a vacation in a far-off place.  This is the sort of thing you dream about, plan for and then some day you go.  We also have a list of things which need to be done by a certain time.  Sometimes this list gets so long you miss deadlines.  The critical list is your short list.  This is a small number of things you want to finish today.  Sometimes your short list never gets hit because somebody else’s emergency bumped you off of it, and you are working on their list.

If you can manage your short list of things to do, then you can minimize the number of times you need to switch contexts, and by doing so you get more done.  When someone contacts you with a task, you need to evaluate that event against your own priorities.  If the event is a true emergency, there is nothing wrong with dropping what you are doing in order to help.  However, if it can wait long enough for you to finish what you are doing, you can more effectively finish your list of tasks.  Better yet, if you can place it further down on your list you can maybe get through your short list on time, saving the new thing for a new day.