Mark looks for investments that can return his share in cash flow. For example, if he invests $100K for a 10% of the company, that means this company needs to be able to make $1M in cash flow to give Mark his money back.

Although this thesis does not guarantee a lot of big exists, it also means Mark is not going to lose a lot of money. He can always work with the entrepreneur to help a business like that to make more money.