The attributes that make great entrepreneurs, the experts say, are common in certain manias, though in milder forms and harnessed in ways that are hugely productive. Instead of recklessness, the entrepreneur loves risk. Instead of delusions, the entrepreneur imagines a product that sounds so compelling that it inspires people to bet their careers, or a lot of money, on something that doesn’t exist and may never sell.

So venture capitalists spend a lot of time plumbing the psyches of the people in whom they might invest. It’s not so much about separating the loonies from the slightly manic. It’s more about determining which hypomanics are too arrogant and obnoxious — traits common to the type — and which have some humanity and interpersonal skills, always helpful for recruiting talent and raising money.

Some V.C.’s have personality tests to help them weed out the former. Others emphasize their toleration of mild forms of mania, if only because starting a business is, on its face, a little nuts.

“You need to suspend disbelief to start a company, because so many people will tell you that what you’re doing can’t be done, and if it could be done, someone would have done it already,” says Paul Maeder, a general partner at Highland Capital. “There are six billion human beings on this planet, we’ve been around for hundreds of thousands of years, we’re a couple hundred years into the industrial revolution — and nobody has done what you want to do? It’s kind of crazy.”

ON a recent Saturday evening, Seth Priebatsch is sitting in his office/bedroom in the 26,000-square-foot space that houses Scvngr (pronounced “scavenger”), which he founded in early 2009. Dozens of toy race cars fill a bookshelf on one wall; the other is covered with lists and drawings. The sofa where he crashes in his sleeping bag lies between the two.

He will explain the genesis of Scvngr, and offer a sort of guided tour of his mind, while sitting on a stool in his bare feet, wearing jeans and a Princeton T-shirt. A pair of Oakley sunglasses are perched, as they nearly always are, atop his head — part talisman, part personal branding.

He is lean, smiley and partial to the word “awesome,” which he uses as a noun — as in “an extra dose of awesome.” He speaks quickly and with what sounds like a Canadian accent, which seems odd because he was raised in Boston.