Gamers have been scrabbling for collectible items since the earliest days of the medium - heart pieces in Zelda, Mario's gold bullion, the glowing rooftop orbs in Crackdown.
In a lot of cases - particularly the old-school platform generation - the reasons behind the inclusion of such collectibles was obvious, at least on a design basis. More items equals more playtime, or extra lives, or a steadily-built defense against enemies. In other words, collecting was essential to succeeding in the game.
More recently, however, games have begun to incorporate collectibles in a very different manner. The scope and ambition of such items has evolved. You don't have to collect all the character biographies in Arkham Asylum or the audio diaries in BioShock - but if you do, you'll be treated to greater story expansion and an all-round more immersive experience.
The thing is: Narrative or aesthetic support isn't enough to explain the phenomenon. Collectibles wouldn't be so ubiquitous unless there was a deeper, more ingrained appeal. Let's take a particularly modern example - the Xbox 360 Achievements system, or its slightly less prestigious PlayStation Trophy sibling. The traditional notion of high-scoring has been cleverly dissected into a series of bite-size chunks; merit-badges that dedicated players can gather, a whole new breed of virtual collectibles. But what is so compelling about all this? Why do some gamers - not all, but many - feel a niggling regret when they see a lacking gamerscore or hear of items that remain ungathered?
Somewhere there's an innate part of us that loves to collect. A motivation. An entrenched reason. A psychological quirk. So - just what is going on in our heads?
Of course, as soon as a subject like this is brought up, there'll be the inevitable lazy outcry: The reason gamers like collecting is because they're nerdy and obsessive, right? We're going to go right ahead and assume you don't need The Escapist to tell you this is nonsense. Nor that such a "collecting is sad" judgement obviously wouldn't apply to your girlfriend's wardrobe full of shoes or your boyfriend's cabinet of football memorabilia.
There is a far more intriguing rationale at work here, and to find it we need to delve into the often-confusing world of psychology. This is something that Jamie Madigan - Personnel Psychologist for the US Government, lifelong gamer and the man behind the Psychology of Games blog - has been doing for years. "The most interesting thing I've found is how easy it is to draw parallels between studies of human behavior in other contexts to people playing games," he explains. "What motivates people to play games are the same things that motivate them to engage in sports, work, art, and lots of other pastimes. There's still a lot that's unique about the psychology of videogames - human-machine interactions, for example - but a lot of what makes gamers tick can be inferred from what's already known about the field."