Long ago, when human knowledge was comparatively sparse and there were no vast armies of academics endlessly pursuing scientific minutiae ultra licitum, smart people could become experts in virtually everything just by reading the key texts. This is one of the reasons there were a disproportionately high number of "renaissance men" during the actual Renaissance than there are today. (Think about it, who was the last genuine renaissance man in human history? Benjamin Franklin, perhaps?) It's not as though human genius is exceedingly rare these days (although, sometimes it's hard to completely discount that possibility when reading the news). The reality is that every course of discipline has expanded to the point where even experts in a particular branch of physics cannot possibly hope to be experts in physics, in general.
This is astounding, when you think about it. The geniuses of yore could be expert mathematicians simply by learning math up to trigonometry or calculus, the equivalent of a senior at a good high school. In the 1700s, if a person understood Newtonian geometry and calculus, one had all the tools required to be a physicist. A couple of additional years spent practicing a musical instrument and acquainting oneself with Aristotle meant that one was a bona fide renaissance man.
Take stock of this. Such men not only had knowledge of important subject matter, but they had deep knowledge of science, literature, art, and philosophy. Today, that knowledge amounts to the totality of what youth learn by about the age of twenty. True, not all of us remember all this information, but most college-educated people must at least demonstrate a temporary understanding of everything that Rene Descartes knew. Many of us must even demonstrate knowledge of even more.
The reason I bring this up is because I have been wondering what I would have to read in order to become a veritable expert in Philosophy. I've been assembling reading lists and trying to identify core concepts that should be understood if one wanted to become, not just a casual reader of philosophical ideas, but an actual philosopher incarnate. The list as it is currently assembled actually appears like a fully reasonable undertaking for anyone with an adult level of reading comprehension and sufficient time on his hands. I leave it to you, the reader, to guess which person might be disposed to such an undertaking.
Naturally, there is more to being a philosopher than reading all the important books and being able to define the important terms from rote memory. A real philosopher must also advance human knowledge of philosophy somehow, or develop new philosophical concepts not previously known.
But one has to start somewhere.