It's polite to replace someone's things you have lost.
Jon borrows his friend's tablet but loses it on the bus home so his friend asks Jon to buy them a new one.
Jon wants to reply to his friend.
Jon agrees with his friend and buys them a new tablet like the one he lost.
Jon says he won't get a new one for his friend because it wasn't Jon's fault it got lost.
Jon's friend respects his integrity and continues to trust Jon with their stuff.
Jon's friend never trusts him with their things again and lowers their opinion of Jon.