Why didn't the curse break when Shrek kissed Fiona?

Question

If the spell breaks at true love's first kiss, then when Shrek kissed Fiona, why didn't she turn human again?

Answer 1

Shrek works it out shortly afterwards. It's not just the kiss that's required, there also needs to be a reciprocated emotional element.

Donkey: Maybe you kissed her wrong?

Shrek: No. The kiss didn't work...because Fiona doesn't love me.