Energy problems are engineering problems, so you would expect to find nerds running cleantech companies. You’d be wrong: the ones that failed were run by shockingly nontechnical teams. These salesman-executives were good at raising capital and securing government subsidies, but they were less good at building products that customers wanted to buy. At Founders Fund, we saw this coming. The most obvious clue was sartorial: cleantech executives were running around wearing suits and ties. This was a huge red flag, because real technologists wear T-shirts and jeans. So we instituted a blanket rule: pass on any company whose founders dressed up for pitch meetings. Maybe we still would have avoided these bad investments if we had taken the time to evaluate each company’s technology in detail. But the team insight—never invest in a tech CEO that wears a suit—got us to the truth a lot faster. The best sales is hidden. There’s nothing wrong with a CEO who can sell, but if he actually looks like a salesman, he’s probably bad at sales and worse at tech.