I believe it's best not to invest just in a specific company or product, but in the founder.
Sometimes, the right person might have the wrong idea; and you might still fund it, just so that founder can get their feet wet and have more experience when they start working on their next idea, where you get first dibs because you funded them before.
Early stage companies: I looked for resourcefulness in the founder and a broad but intelligent perspective on the market combined with humility/coachability.
B and up: traction and systemic approach to scaling.