When my wife and I first moved into our current house, we employed a local gardener.
He was a very nice fellow, very happy and cheerful, but he knew nothing about gardening. He was very good if you gave him detailed instructions, and would work hard mowing the lawn or trimming the hedge. However anything that required decision or judgement, was risky.
There was the day that he weeded out all of the newly-planted border plants. There was the day my wife left some house plants by the car to take into school, and an hour later found them all planted out in the garden. There were many other examples of small scale garden disasters, and eventually we realized that we would have to replace him, as both of us work fulltime and are not able to supervise a gardener to the level that this guy required.
Now we have a new team of gardeners. They are highly knowledgeable. We can give them a broad direction, such as “tidy up this border” or “prepare this area for soft fruit”, and they will do it, often adding bits that we had never considered, or giving us useful advice along the way. Sometimes they will even say “No, we shouldn’t be doing that, that’s not going to work; we should do this instead”.
The new team costs more than twice as much, on an hourly basis, as the first guy. That’s because they are knowledge workers, and he effectively was a Manual labourer.
The simplest definition of a knowledge worker is “somebody who knows more about their job than their supervisor (manager/customer) does”. So instead of you providing the knowledge and they providing the labour (gardener number one), you provide the direction and they provide both the knowledge and the labour (gardening team number two).
The first guy was not a knowledge worker, and we had to tell him in detail what to do, and sometimes how to do it. The current guys sometimes tell us what they should be doing, and always know better than us how they should be doing it.
Also in this we can see the value of the knowledge, represented by the difference in the two hourly rates. The asset that the new guys bring is their knowledge, and we need to pay double the base rate in order to get access to it.