Here is an interesting study. In a survey of academics (really graduate students and academic staff), it appeared that maximum number of different pieces of information (variables) people could keep in mind was: four. That's not much. It seems that when we have to juggle lots of data (for instance researching on different sites on the Internet, different opinions etc.) we are successfully 'chunking' information into smaller bits. They say: "It is a major function of expertise to recognize higher-order variables that relate chunked representations of lower-order variables".
Maybe part of the drive of many great thinkers toward simplicity? They may be reviewing much, but still shifting data into a few cohesive bits of information that fit into a unified whole.
How Much Can Your Mind Keep Track Of?- Press release
How Much Can Your Mind Keep Track Of? Article