People should not ruin other people's belongings.
Carlos is a field worker in Central America and has a very dull machete when his friend offers him a sharpener.
Carlos wants to sharpen his machete.
Carlos uses the sharpener to put a fairly sharp edge on the machete, then gives it back.
Carlos spends the entire night sharpening the machete to a razor-fine edge and wears out the sharpener.
Carlos' friend lets him borrow the sharpener whenever he would like, improving Carlos' work.
Carlos' friend loses his sharpener and doesn't trust anyone to use his equipment properly.