Let's talk about can't a moment.
A long time ago, when David Letterman still looked almost-young, Grace Hopper cut wires the maximum length an electron can travel in a nanosecond. She did this to illustrate to senators and other important people why a computer can't communicate with a satellite faster than the speed of light. It's a law of physics we haven't figured out how to break yet. When Grace Hopper says we can't speed up communications with the satellite, she means we can't speed up communications with the satellite.
If you tell me that we can't do something, my gut expectation is that you'll follow your statement with a mention of the natural law that we'd be violating otherwise. We can't break the speed of light. We can't prevent quantum tunneling. We can't mine more of a mineral than exists.
And yet lately, both in public discourse and my private life, I've heard a lot of people say "I can't [X]" and leave it at that, with no explanation.
We have so many more options to describe our actions, the vast majority of which make us easier to understand. Being transparent about why we're turning away a request or a requestor builds trust. It makes our priorities, needs, and goals clearer to those we communicate with.
That doesn't mean we should do everything we're asked to do. We shouldn't do things that are morally wrong, illegal, or stupid. I'm not redesigning the vendor product's interface because we don't own it.
There are other things we won't do, because of our own priorities, the priorities of our employers. I'm not working sixty hours a week for six months, because I prioritize my mental and physical health over whatever you're offering.
There are plenty of things we don't have the authority or don't have the resources to do. Oh, the things I could do if someone gave me both authority and resources...
Like Bartleby the Scrivener, there may even be things we prefer not to do. I prefer not to run focus groups, not because I don't have the skills, but because there are other kinds of work I prefer.
And please don't get me wrong: I'm not saying that we can't say "can't" unless we're talking about scientific or engineering problems It's part of our language.
I am saying that when we tell someone we can't do something, and offer no explanation for why a thing can't be done, we're selling ourselves short, we're selling the person we're talking to short, and we're selling the relationship short.
And we may be missing out on a great opportunity to illustrate a nanosecond.