My sister Kate and I were seventeen, twins, and in our junior year of high school. That's where our similarities ended. She was popular, athletic, outgoing, and had lots of friends. I was her polar opposite: nerdy, socially awkward, only a handful of friends. Pretty much irrelevant in our school's world. The only thing I knew I had going for me right from day one of high school was my brain. I was smart. Really smart. Top...