Are you critical to your company's success? REUTERS/James Glover II In his 2015 book, "Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future," Ashlee Vance shares the story of how Musk stopped working with his longtime executive assistant in early 2014.

According to Vance, the assistant, Mary Beth Brown, asked Musk for a significant raise after she'd been working with him for 12 years. In response, Musk told Brown to take two weeks off, during which he would assume her responsibilities and see whether she was critical to his success.

When Brown returned, Musk told her he didn't need her anymore.

Musk also told Vance that he offered Brown another position at the company but that she never returned to the office after that.

Musk has since tweeted that the anecdote is "total nonsense."*

He continued: "Mary Beth was an amazing assistant for over 10 yrs, but as company complexity grew, the role required several specialists vs one generalist."

"MB was given 52 weeks of salary & stock in appreciation for her great contribution & left to join a small firm, once again as a generalist," Musk said.

The idea of proving your worth to a company through a test of this type is pretty extreme, but it's a solid lesson in knowing what you're worth to your organization.

Business Insider spoke with Lynn Taylor, a national workplace expert and the author of "Tame Your Terrible Office Tyrant: How to Manage Childish Boss Behavior and Thrive in Your Job." She shared a few strategies for assessing your value — before someone else does it for you — and boosting it.

First, Taylor said, you'll want to do an "audit" of your responsibilities. Take 15 minutes one day to think about what exactly you're working on.

"Could a temp do what you're doing and keep your boss happy?" Taylor said. If the answer is yes, or even maybe, you might need to step up your game.

Above all, Taylor said, "you want to make your boss need you — not just have you on board." So consider what makes your boss successful and how can you align yourself with that, she said.

Some people call it "managing up" — it's about figuring out how you can make your boss look good to their boss.

One tactic is to flat-out ask your boss whether you're adding enough value to the organization. You don't even have to wait for your next performance review, Taylor said.

While you're discussing some other project, you can say: "By the way, I want to make sure that I'm really providing the most value-added work that I can. I know you have a lot on your plate — are there any areas that I could work on, on my time, that would help make your job easier?"

Come prepared with specific examples of how you could help. For example, let's say you know your boss has been working on a tough project, and that you have some solid research experience from your past job that could be an asset to this project.

You could tell your boss: "I noticed that you were working on XYZ. I know that my background in X might be able to take care of some of the more routine aspects of that, but maybe even some strategic aspects of that. I'd love to give it a shot if you're open to it."

The bottom line is that you want to make yourself an integral part of your boss's success — and the company's. What happens after that is out of your control.

"No one is indispensable," Taylor said. "It's just to what degree are you harder to replace."

*This post was updated after Elon Musk responded to the details.