In business as in life, we encounter situations that make us feel negatively or positively. In fewer places is this more apparent than the entrepreneurial space, where roller coaster emotions associated with the freedom of owning ones own enterprise makes themselves apparent from day one. Entrepreneurs are masters of their own destiny, and as such have the ability to change course on a whim. The following article and paper have some illuminating thoughts on the nature of optimism and pessimism as an entrepreneur.
http://www.entrepreneur.com/management/managementcolumnistscotthalford/article207648.html
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.147.6198&rep=rep1&type=pdf