Person A leaves a pile of paperwork by the shredder for a couple of days.
Person B gets fed up of waiting for it to shred itself and does the job, jamming the shredder in the process.
B informs A they have done the dirty work, now A can unjam the shredder as B sure isn't going to.
A says no, you broke it, you fix it.
Who is more wrong/right? A for not finishing the job in the first place or B for leaving the machine out of order?
Which would annoy you more?