The CAR Approach
One struggle we are frequently asked about is what to do when, in their words, "You have a ringmaster that thinks you can get it ALL done." It is true that people have unrealistic expectations of us, and it may seem that they are not sensitive to our current workload. One approach that may help you get to the truth is by using the CAR technique.
C is for Communicate. Ask yourself this question: What percentage of your workload do you think your boss or supervisor knows about? 75%? 50%? Even lower? So, let's look at it from their perspective. They don't know everything on which you are focused, so adding one more thing doesn't seem like a problem. When you are struggling under the weight of your workload, it is important to communicate what you are working on to your boss. This doesn't mean that you whine or complain. It simply means you let them know your workload so they can make better decisions (that's why they are the boss) about where and how to send along work to others.
A is for Ask. You should ask for help with prioritizing or reprioritizing your workload to accommodate this new request. Questions like, "How does this new assignment compare in importance to my current focus?" or "Knowing my current focus, what do you see as something I could reduce my time on so that I can focus on this new task?"
R is for Resources. With any new request made of you, you should ask for additional resources to complete the task. Resources could be assistance from someone else, additional time to complete another project or even physical space to create something. A good circus would never expect a new act to be performed without having to expend some type of resources to make it successful.
Above all else, remember this: If you aren't comfortable talking with your supervisor or boss about your workload, there's probably a bigger "elephant" in the room that needs your attention.