John Watson knew when he somehow fell into an alternate universe where he was a Bond Omega dating Robin Hood, or possibly if Molly was to be believed a demiurge of chaotic good. That he liked it was unreasonable, irrational, and a bit not good.
Sherlock Holmes knew the precise moment when he pair bonded. Three retorts and a biological impulse.
Irene Adler knew when love died. She spent all her days plotting to salt and burn the earth where it still.