When Checking Never Feels Like Enough

Police officer, 46. Cannot sleep since he realised he has been checking the front door exactly eleven times every night for three years - and that this number must never change. He knows it is irrational. He checks anyway.

Marketing director, 33. Rewrites every client email at least four times before sending. Her team calls it perfectionism. She calls it a prison she does not know how to leave.

Student, 22. Must arrange his textbooks in a precise sequence before he can open any of them. He failed two exams last semester not because he did not know the material, but because he ran out of time to begin.

Mother of two, 38. Cannot pass a kitchen knife without an unbidden image of harm. Has hidden every knife in the apartment. Has not cooked in three months. Tells her children she is on a diet.

Retired teacher, 61. Drives back to school three times a week - since retirement - to check that the gas is off. It never has been on. She goes anyway.