A thoughtful request makes cooperation possible without making refusal costly.

Every request carries a shape as well as a content. Asked in front of others, at the last minute, or with a justification that makes refusal look unkind, it can be answered yes by somebody who wanted to say no. That kind of yes is expensive, because it costs them and teaches them to avoid the next conversation. A good request leaves both answers survivable.

Ask in private, ask early, and say what you will do if they cannot help. Then leave a silence long enough for a real answer to fit inside.