Are there character traits that most highly successful people share? Yes, according to George S. Everly Jr., psychologist and professor at Johns Hopkins School of Medicine. With 45 years of experience at leading universities, he's had the chance to observe ultra-successful people before they got that way. And these people weren't all college undergraduates, he writes in a recent Psychology Today blog post. "Rather, they have been graduate students, entrepreneurs, business executives, physicians, nurses, attorneys, veterinarians, and medical students--and yes, those who would become the rich and the famous."

Surprisingly, he writes, highly successful people all seem to share seven qualities that make them unforgettable--even before they become hugely successful. You can find the full list of those qualities here. These are some of the most important.

1. Optimism.

We've all met people who work really, really hard to project an aura of optimism and positivity. That usually feels as fake as their pasted-on smiles. But people who are genuinely optimistic usually can't help spreading that sentiment to others around them. "We feel better just being around such people," Everly writes. If you give presentations or pitches, think back to the times you did so when you were in a really good, optimistic mood. I'm betting that your audience was more responsive and more interested in hearing more from you than other times. At least, that's always been my experience.

Besides making you unforgettable, research suggests that optimism can help you live a longer, healthier life. So if you're not an optimist already, there's ample reason to try and become one. Fortunately, there are some techniques that can help you train your brain to become more optimistic. If you're more pessimist than you'd like to be, give them a try.

2. Trustworthiness.

As Everly notes, it's sad but true that if you show up when and where you said you would, and do everything you said you would do, you'll stand out from the crowd because few people are dependable, especially if they're dealing with strangers or the stakes are low. You'll make even more of an impression if you take responsibility for your actions and for their consequences if things turn out badly, particularly if you're forthright about whatever you did wrong, rather than trying to cover it up. People who do this "take our breath away," Everly writes. "They are unforgettable."

3. Tenacity.

It's hard to become highly successful without this particular trait. Most of us hate to fail, and hate to hear "no." But that hatred keeps us from pushing ourselves outside our comfort zone and going after the things we truly want, even if they don't work out at first.

Nearly every account of a highly successful entrepreneur includes some description of how that person persevered in the face of rejection, or went beyond the norm to figure out how to make his or her company work. When Joe Gebbia and Brian Chesky had maxed out all the credit cards they could to start Airbnb, they could have given up, but instead came up with an obviously crazy idea: Because they were in the middle of the 2008 election cycle they repurposed existing 500 boxes of cereal into "Obama Os" and "Cap'n McCains" and sold them for $40 each. That helped with the immediate funding emergency, but of course they needed more, so they applied to Y Combinator. Y Combinat​or founder Paul Graham granted them an interview, but just couldn't fathom the idea that people would pay to sleep in other people's homes. As Gebbia and Chesky were leaving, though, they gifted Graham with a box of Obama Os and explained how they'd used it to help fund their company. On the ride home, Graham called to offer them a slot--not because of their idea but because he figured founders who could find a way to sell a box of cereal for $40 would also find a way to make their website successful. And of course he was right. 

There are a lot more qualities that go into making highly successful people unforgettable, even before they've achieved their successes. But these three are a pretty good place to start.