Final answer:
The missing factor for determining the viability of a business opportunity is 'projected cash flow.' investors use personal knowledge of the management team and the business plan to assess a startup's potential while founders' investment indicates their belief in success.
Step-by-step explanation:
Factors that aid in determining whether or not a business opportunity is viable include market size, projected cash flow, management skillsets, and passion. When evaluating a startup, the ability to generate a positive cash flow is crucial. A startup's potential for success is often gauged by angel investors and venture capitalists, who seek to understand the business plan and the dedication of its founders.
These investors contribute capital, which is a critical factor of production, alongside entrepreneurship, labor, and land. Founders showcasing their commitment by investing their own money, along with a strong management team, can significantly enhance a business's ability to attract capital and succeed.