You have a junk drawer full of stuff you might use some day. You have a few things that you know you'll never use again, but can't bring yourself to throw away. You have a collection that's too much and too big for the space you live in. So what makes you different from a hoarder? Not much.
Hoarding Isn't Just One Illness
Hoarding is generally listed as an obsessive-compulsive disorder. It's true that a great deal of people with obsessive-compulsive disorder are also hoarders. Obsessive-compulsive disorder and hoarding both run in families — sometimes at the same time.
But sometimes not. While most scientists believe that hoarding is one aspect of obsessive-compulsive behavior, others disagree. The disorders can manifest together, but so do obsessive-compulsive disorder and depression, or hoarding and anxiety. There are major differences between what emotions steer an obsessive-compulsive and a hoarder. While both feel a drive towards certain behaviors, people with obsessive-compulsive disorder feel the need to wash themselves, or lock their doors, or perform other rituals, because of thoughts that intrude on their daily lives. It's a negative feeling that they assuage through ritual. Hoarders, for the most part, feel great when they're collecting things. The acquisition phase of the disorder is fun and recreational. They generally feel neutral towards things they have already acquired. It's only when they are asked to throw anything out that they feel that compulsive drive to do something they know isn't healthy.
Even different kinds of hoarding might be different disorders. Animal hoarders tend to be mostly women, while regular hoarders are a bit more likely to be men. Animal hoarders have markedly different behavior from other hoarders. While nearly every hoarder specializes in a "collection" of certain types of objects, most hoarders keep everything. Animal hoarders generally collect exclusively one type of animal, without feeling the need to hoard anything else.
Hoarding Evolves Slowly
The "recidivism" rate for hoarders is around %70. This is why hoarders get fined again and again for filling their houses and yards with junk, and animal hoarders get sent to jail and come out only to collect more animals.
The process starts in childhood, with a tendency to collect things. It ramps up with the ability of the hoarder to keep collecting. When people reach adulthood they get their own space to fill with junk, and they get money to buy the junk. What usually stops them from going overboard is the other people in their life — family and friends notice things piling up., neighbors dropping in, co-workers take note the state of a person's clothes, even if they never notice the state of their house.
Sooner or later, with hoarders who truly can't help themselves, the people in their lives fall away. Some die. Some move away. Some just distance themselves. Eventually there is no check on anyone's ability to hoard, except the state penal and psychiatric system.
Hoarding Is An Amplification of What We All Feel
Hoarding has been made the subject of many articles,and some riveting television, because it's one of the most understandable compulsive behaviors. Nobody reading this lacks their version of a hoarder's cache, whether it's a stack of old books that we're not going to read, a long Netflix queue we're not going to watch, or a drawer full of cords, adapters, chargers, and remotes that we're never going to sort out, we all cling to something.
There are analyses of hoarding from a social standpoint. As consumerism grows, we invest our possessions with more and more value. We even become convinced our possessions have attitudes and feelings, which is a delusion common among hoarders. (Toy Story, which turned inanimate objects into feeling things that dreaded being thrown away and could retain feelings even when broken, is probably responsible for a few young hoarders.)
Most importantly, brain scans of hoarders have shown that when considering whether to throw things out, hoarders have an unusual amount of activity in the orbitofrontal cortex and the anterior cingulate cortex — both areas of the brain involved in decision-making. Everyone's brains light up when we consider throwing things out. What if I need this later? Can't there be some other use for it? But it reminds me of my great aunt! A hoarder's brain lights up intensely for everything.
Whenever you decide that you'll definitely use that screwdriver again and let it drop back into your junk drawer, you're experiencing what a hoarder feels for everything they've ever possessed. We don't approximate what they feel, we feel what they feel. We just feel it for fewer things.
[Via A Comparison of Object and Animal Hoarding, The Objects of Desire, Hoarding In Obsessive-Compulsive Disorder, Step Inside the Real World of Compulsive Hoarding, Why Do You Hoard?]