A favor should not expand quietly after the person has committed to it.

Agreeing to help is agreeing to something of a particular size. When the task grows afterwards, a lift becomes a whole day, a look at a document becomes a rewrite, the person is stuck: refusing now feels like withdrawing help they already promised. Most of this happens without any intent, because the true scope only became clear later. But the cost of that discovery falls entirely on the one who said yes.

If a favor you asked for has grown, say so and re-offer the choice. If you are the helper, name the new size out loud rather than absorbing it.