It has long been a maxim, in some circles, that 90% of people are not good at their jobs. Over time, this appears to hold true enough to almost be axiomatic.
This rule is often been interpreted as "90% of people are bad at their jobs", which is not necessarily true. To be good at their job, a person must a) have skill and b) care about their job. Meeting neither a) nor b) does not make a person a bad worker, but it guarantees they are not a good worker.
Where do people fail to be good at their jobs? By not having skills or by not having pride in their work.
Skill
In general, people stop learning new skills when they feel secure. The type of person that continually learns new skills is an exception and should, if possible, be kept on staff or on retainer permanently.
Why is learning new skills important? Well, consider the alternative. Your doctor has not learned a new skill since he graduated medical school 30 years ago -- do you think he can make informed decisions about your medical treatment? Your lawyer has not learned of any changes in legislature since he started his practice 10 years ago -- do you want him to advise you in court? Your software architect has not learned a new programming language since he graduated college -- do you trust his judgement in designing your next-gen product?
If someone cannot be bothered to stay up-to-date in their field, they cannot be relied upon to do good work.
Pride
Ask around, take an informal survey of your co-workers, find out why they are doing this particular job/career. If you work at a company of any decent size, or really any company that does not reward creativity or personal accomplishment, then most of answers will be along the lines of "I don't know", "I have rent/mortgage/car/kids' school to pay", or "my parents forced me to".
Why is this? Most people find their work uninteresting and unfulfilling. In fact, most people find the concept of work uninteresting and unfulfilling. What would they rather be doing? Many cannot say, but it sure as hell wouldn't be work.
Pride or care in one's work may seem like a silly or even unrealistic demand. Far from it. Ask yourself the following: Who would you rather have as a doctor -- someone who takes pride in his work, or someone who doesn't? As a mechanic? As a lawyer? As a councilman? As a contractor? As an insurance investigator? As a mailman? As a cook? As a local constabulary? As a gardener? As a DMV clerk? As a cashier?
It is difficult to find any profession where it is not preferable to have pride in one's work.
90-10
The defense given by people in the 90s is generally somewhere along the lines of "what I do isn't that important" or, even worse, "I work hard enough that I deserve to be cut some slack". The first is irrelevant and the second is always patently false. Always reach for a weapon when someone's argument relies on the phrase "I deserve".
Why is the 90-10 rule important? Actually, it's not. It's offensive, which is a lot of the fun, and it takes a bit of the frustration out of dealing with the incompetent ("ah well, you know what they say, 90% of people suck at their jobs"). Ultimately, like most made-up statistics, it is simply a rule of thumb to be applied when dealing with others in a professional capacity.
