There is a commonality that binds the cartoon characters of Walt Disney, Nickelodeon, Warner Bros., and many others from Western animation: the majority of them only have four fingers. The history of four-fingered cartoon characters is about as long as the history of animation itself, and it has become such a ubiquitous trope that people rarely stop to wonder why cartoon characters always have four fingers rather than five. It can be seen in some of the greatest animated series ever made, and even in cartoons created by animation legends like Walt Disney and Tex Avery.
It isn't a rule set in stone by any means, but for over a century, it's become a common practice among animators in the Western animation industry. It has caused some problems for studios, however, when they attempt to export their cartoons, as four-fingered cartoon characters are taboo in Japan. Despite this, the characters can be adapted for specific markets. Many cartoons have evolved over time, but the four-fingered phenomenon has remained constant.
Cartoon characters were traditionally limited to four digits - three fingers and a thumb - and the case has remained since the earliest days of animation. Before any form of computer-generated imagery (CGI), creative teams made all animation by hand. It was an incredibly arduous process, and animators were willing to take shortcuts to lessen their workload, as long as the finished product wasn't negatively affected. Cartoonists could significantly reduce their amount of work by getting rid of one finger from each hand of a character.
A standard animation runs at 24 frames per second, which requires 24 separate drawings within every second of the animation's runtime to create the illusion of smooth movement. For reference, one of Mickey Mouse's earliest appearances was in 1928's Steamboat Willie, an eight-minute short. To make those eight minutes, Walt Disney and his fellow animators had to make 24 drawings per second with 60 seconds per minute, thus totaling about 11,520 separate pictures.
In finished animations, four-fingered hands are practically indistinguishable from those with five-fingers unless carefully examined. So to expedite the animation process, animators repeatedly drew one less digit, and the practice carried over when computer animation became prominent.
Since early animators were already taking a shortcut by reducing the number of their characters' digits from four to five, why not cut it even further down? Well, anything less than four does not appear human.
Whereas a four-fingered cartoon character can easily pass as a facsimile of a person, three-fingered beings appear inherently alien. Our brains are able to process four fingers and understand it as being close enough to a real human hand, and it's not distinct enough from reality to the point where it becomes disturbing. It's hard for our brains to accept three-fingered people in animations. And though three-fingered cartoons do show up occasionally, it's only when the character is intended to be non-human, or the design calls for a lack of realism.
People have the innate ability to recognize other human beings, but when something is modeled to resemble a human but comes short of doing so, it produces a feeling of uneasiness for the onlooker. The latter is referred to as the "uncanny valley," which works on a spectrum. When human beings are produced - or modeled in some form - in animation, audiences tend to enjoy realistic reproductions.
At some point when the model looks close to being human but is missing some minute details, our enjoyment drops and the model takes on an eerie vibe. The model may appear similar to a person, but because there are incorrect details, it no longer seems human but a mere imitation. It's the same reason why so many people find modern, lifelike robots to be so frightening.
Four-fingered hands work on this same spectrum; they are close enough for people to accept they are human or "humanesque," but not so close to reality that audiences find them disturbing.
Animation and character design rely heavily on basic geometric shapes. The fundamental design and configuration of a character can give insight into a character's personality and create a thematic basis for them. Early animation is identifiable for its use of circles as the basic geometric shape, as apparent in characters like Mickey Mouse, Felix the Cat, and Wimpy from Popeye.
Animators usually exaggerated and rounded simple shapes, and for that reason, this caused problems when designing hands. The prevalence of circles made thin, delicate fingers even more challenging to draw. Walt Disney commented about creating hands for Mickey: "Using five fingers would have made Mickey's hands look like a bunch of bananas."