Never know, I've had a new client walk in who had not filed for 11 years, and since he was self-employed, I really did need to do them all. Thanks be, he actually had decent records. I never really knew why he did not file, except that he had losses for the first years, and did not figure he needed to file when he would not owe or get a refund. By doing them all, we established his basis, depreciation, etc. He was a great client from then on, and the fees for those returns, and dealing with the IRS for him, sure was nice too.