Last week a customer told me that strange things were happening and that his wife dismissed his concerns as paranoid. He recounted two recent incidents of people rifling through his car and gym locker without apparently stealing anything. In most cases I don’t dare tell a customer I think he is experiencing paranoid (or “persecutory”) delusions, especially when I’m pretty sure it’s the case. It can only lead to trouble. But this was a very smart immigrant working for a major software developer and it did not sound like he was describing a longstanding issue. I told him that if people close to him were suggesting he has paranoid delusions, he should be aware that it’s an actual diagnosable problem and should consider what they were telling him rather than allowing a small thing to become all-consuming.

Once I arrived at a client’s apartment door for an appointment and had to knock, ring the doorbell, and call several times before he arrived at the door in a bathrobe. He apologized and explained that he’d been in the shower and didn’t hear the phone ring because of the radio. Indeed, it was blaring. I asked him to turn the stereo off so I could talk to him. He clomped over to his stereo to turn it down and then clomped back over to me. Then he dove into a long saga about how the girls in the apartment below him—recent college graduates—were terrible neighbors and had been harassing him relentlessly, breaking into his apartment and causing all kinds of mischief. As he told me this, he continued to stomp around the floor of his apartment. He was trying to drive the miscreants below to move away. They were the worst neighbors, he insisted. The previous week his surveillance camera had caught them skulking around inside his apartment while he was at work. Alas, he accidentally deleted the footage before he could turn it over to the police.

I had another client who sold her house and moved to a different city because she was fed up with her neighbors breaking into her home and stealing random items like car insurance bills, one shoe from a pair, and can openers. She’d spent a fortune having high-security locks installed on her exterior and interior doors, and then having them rekeyed over and over again. She would roam around her large unheated house with a passel of keys hanging from a lanyard around her neck, searching through them to find the right key to get into each room.

Another client was convinced that someone had broken into her house and left a glass in the sink. It was probably an ex-boyfriend, she thought. A different customer had just installed an expensive new lock but was convinced that her imaginary persecutors had tampered with it to make it slightly less resistant to lockpicking. Someone else called me to change her locks for the second time in a month because an electric blanket went missing from her bedroom closet.

There are certain commonalities in all of these cases. The imagined antagonists never seem to steal anything of value or do anything to threaten the health or livelihood of the victim. The violations all seem pointless. The subjects are normally employed with regular jobs, though some are a little eccentric and many tend to be hoarders. They often point to barely visible scratches on windowsills and doorframes as evidence of furtive entries. They usually have a clear idea of who the perpetrator is.

In all cases, they are genuinely suffering. It’s a devastating condition to have. People who imagine repeated victimization at the hands of mischievous home invaders feel the same range of terrible emotions that anyone does after a home is broken into. But they experience it over and over again. And what’s worse, the people closest to them don’t believe the stories and get tired of hearing about the problem. It can ruin relationships and leave people isolated from friends and family.

When I encounter these cases I try to come up with cost-conscious ways of making the customers feel more secure, but resist requests to repeatedly rekey their locks. I prefer to avoid customers who are experiencing paranoid delusions. If I were less scrupulous I might lick my chops at the fount of repeat business, but I’d much rather spend my time doing useful work than taking advantage of someone’s mental illness. Plus, I’m often concerned that a misstep could cause them to turn their suspicion toward me. More than anything, these customers make me feel kind of useless. Dozens of times throughout the week I’m presented with real issues that I’m able to completely resolve. This is one that I’m helpless to do anything about.