In the bodybuilding world, they say "no pain, no gain." Applying that same principle to investing, you could say, "no risk, no reward."
High-risk, high-reward opportunities in the stock market usually come in two different forms: early-stage growth companies that don't make profits and mature companies disrupted by change that are embarking on a turnaround plan.
In today's market, many of the small, unprofitable growth companies trade at very high valuations, which might take away some of their future upside. Therefore, most high-reward opportunities today seem to lie in the beaten-down deep value stocks of companies undergoing turnarounds.