In the most memorable scene from the movie "Hidden Figures," Al Harrison, played by Kevin Costner, uses a crowbar to knock down the "Colored" sign outside a segregated bathroom after learning that human computer Katherine Johnson has been walking half a mile across the campus and then back several times a day because she's not allowed to use the whites-only ladies rooms in the building where she works.

In fact, this is a bit of Hollywood fictionalizing. Al Harrison is a made-up character, and the real Katherine Johnson says she went a long time without realizing she wasn't supposed to use the white ladies rooms, which weren't labeled one way or another in the building where she worked, most likely because in those days of segregation, black people were only supposed to be working on the other side of the campus. When someone finally told her she simply ignored that information.

But even if the story of Al Harrison and Katherine Johnson isn't true, it can teach you an important lesson about the difference between a mentor and a sponsor, and why having a sponsor is even more important. That advice comes from leadership coach Daina Middleton, author of Grace Meets Grit: How to Bring Out the Remarkable, Courageous Leader Within. In the NASA depicted in the movie, she says, "These women could never have gotten to the point to do what they did if a man hadn't stood up for them."

A mentor, who may or not be part of a formal mentoring program, gives you helpful advice. A sponsor gives you public support, and advocates for you and your projects with others, Middleton says. That means your sponsor has skin in the game. Your poor performance will reflect badly on your sponsor, whereas if you shine, he or she will benefit from having supported you. "The real distinction is that other than dedicating time, there's no skin off my back to be a mentor to someone," Middleton says. "That's very different from a sponsorship standpoint."

You need a sponsor, or preferably several sponsors, to achieve success, she says. Here's how to get one:

1. Choose someone you already have a relationship with.

Someone who doesn't know you or your work that well is unlikely to take the risk of sponsoring you. So choose someone who's familiar with the role you play and your best work. "It should be someone you've worked alongside and developed a rapport with," she says. "It should be someone you trust who has a good idea of the value you bring."

2. Make a very specific request.

"Organize your thoughts," Middleton advises. "Ask for a specific action you want that person to take." For instance, if you're seeking a promotion or making a pitch for a project you want to do, or you're about to meet with a big customer, ask your sponsor if he or she would be willing to make a call beforehand and lay some groundwork for you.

This is a lot better than asking someone, "Will you be my sponsor?" Middleton says. That question is likely to make people uncomfortable and hesitant, since they won't know what they're committing to.

3. Get in the habit of asking for return favors.

When someone asks you for a favor, get in the habit of requesting something in return, Middleton advises. That doesn't mean you should only help people who can help you in return, but it is how strong business relationships are built. Most people are more comfortable asking for something if they know they can give something back. Often, that something might be a show of public or private support.

4. Think small.

Unlike mentorship, which can last for decades or more, sponsorship relationships are usually short-term, related to a specific project or function, what Middleton calls "situational sponsors." Consider asking for sponsorship even for relatively minor pitches and projects, she says. "That's the way to start--by thinking about it in bite-sized chunks," she says. "You're not asking someone to defend you for life."