According to Tom Darden in a great interview I recommend
I don’t like to be involved with things where if you were successful with it, it wouldn’t move the needle. A lot of things fall into that category. In life, or business, or dealing with the environment. My goal is to work on things that at least if you were successful, they matter.
Tom Darden runs the “North Carolina-based Cherokee Investment Partners. Cherokee is a private equity firm specializing in the acquisition, remediation and sustainable redevelopment of brownfield real estate properties. Bloomberg.com specified that the firm typically made a minimum investment of $25 million.“