Just being the CEO of a real, growing company is a huge accomplishment. Starting a thriving business is massively difficult, so if you've managed to get one off the ground, you've already demonstrated a high level of acumen and skill.

But what is it that allows some leaders to rise even higher, building truly exceptional companies and setting themselves apart even among the already-impressive companies that run America's startups?

That's what one poster to question-and-answer site Quora wanted to know recently, asking "What separates the top 10 percent of startup CEOs from the rest?" The curious question asker must have struck a nerve as he or she spurred some truly impressive names from the world of startups to weigh in, including top investors, CEOs, and veteran scene watchers. The complete thread is worth a read in full if you want to take in the entire spectrum of opinion, but if you're wondering what common themes emerged across answers, here are five.

1. Resilience

The first essential skill is perhaps the least controversial--the ability to survive and adapt to the (many) inevitable ups and downs of startup life. "AirBnB took 1,000 days for its business to start working. Imagine if they gave up on day 999? The best CEOs find a way to dig in and keep going even when it seems everything is going against them," writes Robert Scoble--who currently studies startups for Rackspace--of the truly top notch leaders he has met.

Top VC Mark Suster, who offers a brief 13-item list of essential attributes of truly great startup CEOs, puts tenacity at No. 1 and resiliency at No. 4.

2. Integrity

You might think that responders include integrity out of a sense of morality or decency. Nope. According to Scoble, the need to have integrity is far more practical than that: "The best CEOs are survivors and it's really hard to survive if you have dirt in your closet or treat people differently behind closed doors than you do in public." Suster, likewise, includes integrity in his list of key attributes.

3. Specific passion

Everyone knows that CEO isn't a job for slackers--to be even mediocre at the job you have to be willing to put some serious time and energy into it. But the best of the best aren't just garden-variety workaholics willing to throw themselves into whatever job is at hand, according to several posters. Truly exceptional CEOs are driven to extreme effort by passion for the particular project they're working on.

Suster calls this simple "passion for what are you doing," while digital marketer R.G. Riles explains that the best CEO he's worked for "loves the premise of the startup so much that he routinely works 80-hour weeks without feeling like he has been working much at all."

4. Craftiness

"Unlike government bureaucrats, startup pros typically cannot solve problems by throwing money at them. This perpetual resource deficit requires creative and frugal solutions that are often counterintuitive and never obvious," reports John Greathouse, a partner at Rincon Venture Partners. In order to thrive with these constraints, an exceptional startup CEO needs to be "wily" in his estimation. Suster may be thinking of similar abilities when he says it's essential for a startup leader to have "street smarts."

5. The gift of gab

CEOs do a lot of two things--deciding and then convincing. You can be great at the first and still not get very far if you're not great at the second as well, so you can get diverse parties, from investors to employees, to go along with your vision. For this reason, responder after responder mentions some form of persuasiveness, storytelling, or conversational finesse as a marker of an exceptional CEO.

"CEOs have to deal with conflicting interest groups. Customers often want something investors don't. So a good CEO is really great at convincing other people to get on board, even at changing people's opinions," writes Scoble, who adds "a great CEO is clear, crisp, concise. Quotable."

"All leaders have to deliver tough feedback, have difficult conversations, tell people things they don't want to hear. CEOs that are skilled at delivering tough messages in a way that the recipient truly hears" tend to stand out, notes Stride CEO Debbie Madden.

What characteristics would you add to this list?