Saying yes is easy when the cost is invisible. An assertive answer names the work, the available capacity and the choice that another person needs to make.
Show the existing commitment
Before accepting a new request, open the actual work plan. Name the deliverable, owner and deadline already in place. “I can draft the client update by Thursday; taking the new deck today would move that review to Friday” gives a colleague something concrete to decide. Avoid a vague “I am too busy,” which hides the trade-off and invites another round of negotiation. Include the time needed for review and correction, not only the first draft.
Offer a real choice
Ask which outcome matters most: scope, speed or quality. You might deliver a shorter brief today, the full analysis next week, or transfer one task to someone with capacity. State what each option gives up. Do not offer an impossible third option just to sound cooperative. If the request is urgent because a customer or safety issue changed, document what work is displaced so the team can reset its other promises.
Close the loop in writing
After a conversation, send a short confirmation: “We agreed to pause the dashboard refresh, publish the two-page brief on Friday and review the full model next Tuesday.” Include who makes the next decision. This is especially useful across time zones and when work passes between teams. The message is a record of the choice, not a defense of your character or a verdict on the requester.
Try it in a real workweek
A designer is asked for a new campaign page while the existing launch is in review. She offers a wireframe for tomorrow or a production-ready page next Wednesday, and asks the launch owner which deliverable should move. The decision is visible to both teams.
Assertiveness is not a substitute for authority. If every request is “urgent” and no one can choose priorities, the organization needs a decision owner and a capacity review.
Check the source and the context
For the next step, see this related field guide.