tl;dr stupid clients with their stupid requirements.

Client: (on Monday) hypothetically could you implement "A"?
Me: (on Monday) yeah I could do that by Friday, let me know if you want me to start it.
Client: (on Thursday) hey remember we talked about "A" well do "B" instead and I'll need it by Friday still.
Me: "B" is completely different than "A" and will take probably twice as long.
Client: but you told me you could do it by Friday.
Me: ............ I want to smash your face.