If you only let oneself (yourself) into your heart, you'll end up mourning all of the loves and friendships you could have had but didn't let in.
While you're in mourning, you feel a sharp pain in your crying eyes. A key (き) comes sliding out with your tears. You look around wildly, but you're still alone. Is this... the key of mourning?
Currently there are no similar looking kanji which exist in the WaniKani learning system