The person doing an unfamiliar task needs time that the experienced requester may forget to count.

Skill compresses time and then hides how much it compressed. Once you have done something two hundred times, the setup, the false starts and the second-guessing have all vanished from your estimate, so you quote the length of the smooth version. The newcomer meets every step you no longer see. Their slowness is not reluctance but the real cost of the task before practice removed it.

When handing over something routine, double your estimate and say so aloud. Ask which step is taking longest, and you will usually find the part you forgot to explain.