A Renaissance man or a polymath is somebody who is very knowledgeable and has various capacities – a multi-talented person. For example, Leonardo Da Vinci was not just a painter, but he was also a mathematician, engineer, inventor, architect, botanist, musician and a writer, to just name a few.
Nowadays, however, there are very few people who can be considered Renaissance men or women. The problem with the modern world is that it has become and, in fact, insists on and demands specialization. No matter what you do or where you work, it is important to “limit” yourself and become a specialist or expert in one particular field or area.
This applies equally to the McDonald's employee and the university professor. There should be ideally one branch of knowledge that you will know really well, even to the point of exhaustion. A PhD is said to give you the ability to know everything there is about a specific given subject. The fast food chain employee will be trained to become most efficient in a particular area of the restaurant.
Why do we have to specialize then? If we look back in history there has not been the wealth of knowledge there is now. That is essentially a good thing. Philosophy in its earlier stages used to be comprehensive and embraced various disciplines in one. For example, biology and medicine, astrology, psychology and sociology, political science and history, all of these academic disciplines evolved out of philosophy. In other words, a philosopher back then was indeed a prototype of a Renaissance Man.
Today, in order to become “special” one needs to be a specialist. If you are the best source on the subject, all the doors will open for you. People will come to ask you for information. Yes, your knowledge will be not very comprehensive, but there is one subject you are an expert in.
In terms of jobs in the fast food chain, it is a matter of economics. By dividing work in different areas and with distinct responsibilities, the employer saves time, his company becomes more efficient, and as a result, there is more profit to be made. So if your boss realizes that you have a natural talent and make damn good milkshakes, you will be the milkshake expert. People will find out and will want to try your famous drink.
In other areas, it becomes, due to the wealth of knowledge, impossible to know everything. There are some very few exceptions though. I think one can consider Noam Chomsky as one of the traditional Renaissance Men who have managed to break through successfully in various disciplines.
Although I have enormous respect for experts in any field (I'll drink your milkshake anytime), I find it limiting, unfulfilling and - well … boring. It is one of my major obstacles towards getting a PhD degree (incidentally called a “Doctor of Philosophy” no matter what the subject). I have no idea in what to specialize as various fields are of equal interest to me. By accepting one and rejecting another, I would be doing injustice to my overall curiosity for knowledge.
Once a friend of mine told me that it is better to speak one language perfectly than to know several well. It was a kind of unusual comment, especially since I often pride myself on knowing five languages, but I think she made a valid point. She was in tune with the necessity of perfecting one area over the drive for general knowledge in various areas. However, I still think I prefer the multi-talented and widely knowledgeable Renaissance man over the brilliant, but essentially limited, expert.