The one-line reply that turns "sure" into a conversation about priorities
It is 4:50 on a Thursday. Your boss stops at your door, or pings you, and says the four words that have ended more evenings than any deadline: "One more quick thing." The quick thing is never quick, and "sure" is the most expensive word you will say all week.
"Sure" fails for a reason that has nothing to do with willingness. It tells the person asking that your plate had room, and it teaches them that it always will. The lines below do something different: they make the trade visible and hand the priority decision back to the person who should be making it.
1. Your boss adds a project to a full week
Tempting: "Sure, I'll fit it in."
Better: "Happy to take it. I'm at capacity with the board deck and the vendor review this week, so which of those moves?"
Why: you said yes, and you put the cost of the yes on the table. Most managers have no idea what is on your plate, and this is how they find out without a complaint.
2. A peer asks you to take a quick look
Tempting: "Send it over."
Better: "I can give it twenty minutes on Thursday. If you need it sooner, who else could take a pass?"
Why: a time box turns an open favor into a bounded one, and the second sentence reminds them you are not the only reviewer in the building.
3. Your boss's boss asks you directly
Tempting: "Of course."
Better: "Of course. I'll let Maria know it's coming ahead of the forecast so we're aligned on timing."
Why: you accepted the work, kept your manager in the loop, and made the two of them sort out the priority. Senior leaders respect the move; it is what they would do.
4. The recurring favor: the notes, the planning, the offsite
Tempting: "No problem."
Better: "I've taken that the last three times, so let's rotate it. Who's next?"
Why: research for the book The No Club found women are asked to do non-promotable work about 50% more often than men, and say yes more often. A rotation turns a default into a system, and systems do not need you to be the bad guy.
5. A 6 p.m. request for 8 a.m. tomorrow
Tempting: silently work the night.
Better: "I can have a solid first version by 10, or the full thing by end of day. Which do you need?"
Why: two real options with real costs. More often than not, the asker picks the one that lets you sleep, because the 8 a.m. deadline was a reflex, not a requirement.
The principle behind all five
Every yes is a trade. Say the trade out loud, and the conversation stops being about whether you are helpful and starts being about what matters most. That is a conversation you win. Notice that none of the five lines contains the word no. You are not refusing anything. You are asking the person with the authority to choose to do the choosing, which is their job, and making it slightly inconvenient to choose badly.
Save this one. You will need a line from it before Friday.