A lot of us have great difficulty in saying no to things. A very common advice to maintain a healthy lifestyle is to be able to say no. However, there are three fundamental problems with requests: (1) they come sequentially and we do not know what is coming in the future; (2) there are multiple dimensions such as interest, relevance, impact, skill level, and personnel, to name a few; (3) the time and resources needed are hard to estimate at the time of making the decision of whether to accept or say no to something. There is an uncertainty or a lack of information that makes the decision a tough one.
Let us look at the above problems one by one, but with some specific examples in mind: (a) your supervisor asks if you would like to work on a particular project on a topic you are not familiar with; (b) you have been requested by your office to take on an additional responsibility of stocking up the kitchen; (c) you have been asked to review a journal article. It is important to add a caveat that at the epoch of making the decision, you do have enough time on your plate to manage the activity. Otherwise this is would take us into a different discussion about how not to take up things when we just do not have the time.
This predicament falls under sequential decision-making under uncertainty which brings us to aspect (1) mentioned above. When your supervisor asks you in situation (a), neither you nor your supervisor knows what is coming next. In situation (b), perhaps a job you would have loved to do, such as organizing a Karaoke night might come up. Also, in situation (c) maybe an article you are more interested in reviewing might show up later. But you can never be sure of what is coming in the future to make a decision here and now. When we have time, we end up saying yes to these as anticipating the future is not easy.
Aspect (2) is closely related to Ikigai, the Japanese principle (see YouTube video) as a path to happiness by doing things: you love, you are good at, you can be compensated for, and the world needs(it is the intersection of all four). However, it is hard to determine without knowing much about the task you are signing up for, whether it would satisfy all four criteria of Ikigai. In case of the supervisor assigning in (a) we would not know details of the task till we are well into it. Something like stocking up a kitchen in (b) might sound interesting and impactful, but you may not be sure what skills it needs.
Finally, aspect (3) about estimating the time a task would take is not easy, especially when you know nothing about it. For example, when you are asked to review an article in case (c), it is impossible to say how long the article is, whether it is highly mathematical, or whether it is written well. So when you agree to review the article, it is hard to estimate the time it takes. In fact, it is well documented that we typically grossly underestimate the time it takes to do tasks. However, if we had a reasonable idea, we could do a much better job of accepting a task by evaluating the time commitment.
So here are some alternatives to consider while making decisions with the understanding that not all will be applicable in all circumstances.
Grouping Decisions
There is a huge benefit in grouping decisions together so that you could evaluate one versus the others to decide which to accept and which not to. So, if at all possible, wait till you get a few asks before you decide which you want to accept and which you do not. That is why in many job applications, college admissions, and grant proposals there is a deadline (and the decision-makers can select from among the candidate applicants). In some circumstances this may be possible at work tasks too.
Renegotiate Terms
The book Factory Physics talks about three ways to manage uncertainty using buffers: inventory, capacity, and time. In the same vein, to fit in a new task we may have to be prepared by asking for an inventory of examples (like computer codes of related problems), asking for help from others (or adding personnel), and asking for more time. In particular, for all the commitments we have, we could go back and revise our commitments, or just discuss with our supervisor about a priority order of tasks, thus buffering time for some.
Not play favorites
One reason some of these decisions under uncertainty are hard is because of regret. We accept or reject things being afraid that we would regret in the future (see hindsight bias that Annie Duke talks about in “Thinking in Bets”). The regret may be because we judge each task way too much like as if one task is worthier than another. Instead, a radical idea is to take up a task if we think we have time for it, but not revisit that decision. We just give our best for every task at hand.