You shouldn't sell someone's belongings without asking first.
Hiroki plays a game with a friend, who trusts Hiroki with his account password and who has some extra items lying around.
Hiroki wants to get some in-game money.
Hiroki asks if his friend could lend him some in-game money.
Hiroki logs on to the friend's gaming account and sells some little-used items, then transfers the money to himself.
Hiroki's friend lends him the money he wants to buy a nice item.
Hiroki's friend get upset as he had been saving those items to trade with others.