This paper develops an endogenous growth model to examine the influence that heterogenous entrepreneurial ability between individuals and between countries can have upon economic growth. Entrepreneurial ability is argued to be a function of the combined influence of societal, psychological, and genetic factors, the net effect of which upon any individual remains difficult to forecast. Failure by financial markets to accurately identify true entrepreneurial ability ex-ante can result in unfulfilled expectations ex-post. Overestimation of true entrepreneurial ability by imperfectly informed financial institutions causes a divergence between fundamental and market values with the subsequent emergence of a speculative bubble – as consistent with the recent US stock market experience. That said, the news isn't all bad. Even though speculative bubbles may result in a mis-allocation of capital from a rational expectations standpoint, there is still a net benefit of knowledge spillovers generating a higher growth outcome even when over-investment exists. Again, this may be consistent with the experience with the recent bubble with the US equity market.