The English idiom give someone an inch and they’ll take a mile means that if you do a small favor for someone, they will become greedy and ask you to do bigger and bigger favors for them. It is a way of expressing that some people are never satisfied with what they have and always want more.
The idiom first appeared in writing in 1546, but with a different unit of measurement (ell instead of mile). An ell was a unit of measurement that was about 45 inches, or six handbreadths. The idiom changed its wording over time, probably because ell is no longer a common measurement.
A similar proverb is one about a camel’s nose. The idea is that a camel was allowed to stick its nose in a shop. Once its nose had entered, it was much easier for the camel to force the rest of itself through. This same idea applies to the expression give an inch and they will take a mile.
