The main idea when you become a quant is that a computer is less prone to pitfalls than a human. Computers and humans are prone to different pitfalls. Humans have far too many biases to count - see for example, the works of Kahneman and Tversky and most of social psychology. Computers, on the other hand come with a whole host of different problems (perhaps because they're made by humans). The essential advantage a hu…
Computers are just the next step, crunching out the patterns until they are unexploitable (below the threshold of trading costs).
The end result is that markets are a random walk - unless you are at the bleeding edge with faster machines, better latency, lower transaction costs, etc.
Of course, an alternative to this is to do true bottom-up analysis, or invest in illiquid companies (like VCs do).