According to a Glassdoor survey, 39% of Americans believe they're earning less than they deserve.

"Women are less willing to negotiate than men," says Robin Pinkley, Ph.D., a professor at SMU's Cox School of Business. "They often anticipate that organizations will accurately evaluate their potential and pay them accordingly."

That could be one reason why women on average earn 82.5% of the median income that men do. Other reasons include women having less work experience and being employed in lower-paying fields. However, if we compare men and women with the same education and in the same positions, the gender pay gap closes to just 3%.

There is another group of people who are often underpaid: young workers. "Millennials tend to have a strong focus on fairness, with the notion that resources should be distributed evenly," Robin says. "As a result, making the ask during negotiations is very hard for them."

You don't have to be a woman or a Millennial to discover that you're making less than your colleagues. If that happens, there are three things you can do: accept it, change it, or leave it.

"It's not [the company]'s fault that you negotiated poorly at hiring time," says Jay Bazzinotti, a product manager and author, "The money they offered you was acceptable to you at the time. The fact that you somehow found out that others get more is not their fault."

However, if you aren't satisfied with your current salary, then you can change it by asking for a raise. "This is most effective if you have become a key player and added positive value," says Jay. "Your best bargaining position is to show them how you will assist them to be successful in the future and how, therefore, it will be worthwhile to increase your pay [because you will leave the company otherwise]."

You should prepare for the possibility that a raise won't be given and, in that case, you might have to give notice--but make sure you leave on good terms. "I urge you to avoid any bitter action, negative outpouring, sabotage, property theft, time chiseling and so on," advises Jay. "Once you are on that road, then they will be forced to fire you."

So, you probably don't want to have alcohol delivered to your office and then publicly criticize your boss for not paying you enough to eat. (Because that will probably get you fired and then you might end up needing to ask for money from strangers on the Internet.

"If you want to attack your boss in public, well, you broke every single agreement you signed on the way in," adds Jason Calacanis, an entrepreneur and early investor in Uber and Tumblr. "Slamming your boss on Medium is a great way to get attention, but Treehouse, Lynda and countless other sites provide a better path."

Jason believes that the frustration that might come with earning low wages can be channeled into positive changes. "It sucks to start your career at the bottom. I was pissed off that I got paid so little when I started, so I added skills all night long reading books about computer networking," says Jason. "I used my anger at making $3.50 an hour to push myself to $5, $8, $10, $15 & then $100. If you learn a skill and apply yourself, you can rise up and increase your hourly rate quickly."

The Khan Academy, a non-profit organization that offers free online courses to over 15 million students, is one way to learn those skills. "With a mission for a free, world-class education for anyone, anywhere, Khan Academy believes in the value of empowering people to learn new skills," Minli Virdone, Khan Academy's Chief of Staff, tells me. "We have over 7000 videos and 150,000 exercise problems in topics ranging from arithmetic, to algebra, to financial literacy, and even art history. People around the world can use our resources to learn new skills to help them prepare for their future careers."

If you don't want to stay at your current job, (even temporarily) because you aren't being paid what you're worth, you should find a way to negotiate a raise. But if you have decided to leave, then you should improve your knowledge and skills so you will be more valuable to your next employer. And, if no one is offering what you want, then create your dream job yourself, such as starting your own boutique marketing firm or healthcare tech startup, as I've recently written about for Inc. Magazine.