Why do we choose a WRONG option in CAT?

With the threat of Negative Marking looming large on our head, we are very careful while marking answers in CAT. Still, we get some questions answered wrongly. Why?

Here are a few Reasons for marking wrong answers:
1. Students know the concept, but in a hurry they mark the wrong answer.
2. The calculation part took more than 90 seconds and still the student is not sure of two options, marks a fluke and gets the answer wrong
3. The student is working at an extremely high speed and the accuracy falls dramatically
4. The student does not know 5 questions in a row and marks randomly in the next question
5. The student's basic concepts of Grammar, Vocabulary, Formula's are not clear

Reasons abound, think of more and put them as Comments to this post