An angel investor who's helped start over 100 companies reveals the No. 1 thing he looks for in entrepreneurs

If you watch "Shark Tank," you know there are plenty of traits and behaviors that can turn off potential investors.

Cockiness, sheepishness, inexperience, idealism - just to name a few.

It's considerably harder to figure out which characteristics attract investors and make them believe in the entrepreneur's business idea.

Even David Rose, a serial entrepreneur and an angel investor who's either founded or funded over 100 companies, says it's hard to pinpoint one specific quality that draws him in. But over the course of his career, Rose has learned to look for one key predictor of success: What have they already started?

Rose is the founder and CEO of Gust, which runs a platform and community for entrepreneurs and early-stage investors. He's also the author of two books, most recently "The Startup Checklist."

The majority of the entrepreneurs Rose meets with are in their 20s and 30s - which he says means they've had plenty of time to come up with an idea and run with it. He told Business Insider:

If you managed to get through a quarter of a century without ever yourself having started something, that's a real telltale sign to me. It doesn't matter what the hell you started, whether it was a charitable drive or a sports club at school or whatever. Show me, tell me, help me understand what you have actually started. Because what entrepreneurs do is they have an idea and then they execute. They get off their rear end and they go do something.

Rose said he's more inclined to invest in an entrepreneur who's taken initiative than someone who's spent years acquiring knowledge without applying it.

"There are a lot of 'wantrepreneurs' out there who are very well-meaning and love the thought of startup companies," he said.

"They know the industry cold; they've read all the books; they know all the stuff; but they've never actually done something. And that is like the killer thing. I would much rather take somebody who has not done all that reading … but instead just went and did something."

Research suggests that serial entrepreneurs are more likely than less seasoned entrepreneurs to succeed in their business ventures - regardless of whether they failed or succeeded in the past.

As Rose said, "having experience being a serial entrepreneur is only either neutral or good. It's not a bad thing, even if you failed."

The takeaway? If you've got entrepreneurial aspirations, don't spend all your time reading and thinking about starting something. Instead, go out and try it - the experience will likely give you a leg up when you're sitting across the table from a potential investor.