When I was about 12, and my brother about 10, one of us1 threw a lump of coal at the other. The coal ricocheted around our living room and smashed an ornament.
In the subsequent inquest, both of us tried to blame the other, as brothers do; he reasoned, perversely, that I had thrown it, so it was my fault. I, on the other hand, used my football refereeing logic to insist that as he'd had the last touch, he was solely responsible for the broken ornament.
I think of this every time someone blames a butterfly for extreme weather conditions, or a refereeing decision for a team's relegation2, or a straw for landing a camel in traction: there's a human tendency to blame the last action rather than the build-up.
This is especially true in exams. Every year, I hear of students missing out on their grade by a mark or two, and then get into a whirlwind of remarks of their last paper, blaming the examiner for not giving them a borderline mark.
It's much easier, cheaper and more reliable to get questions right, and write the answers clearly. Honestly. Examiners aren't evil - they just have a huge amount of marking to do, screen glare, time limits and all sorts of stress. If you make their lives easy, they'll love you for it - and the borderline marks are more likely to fall your way.