One CEO and former Googler says this is the No. 1 biggest mistake job seekers make

Nobody's perfect. We all make mistakes. And this is especially true during a job search.

Liz Wessel, CEO and cofounder of WayUp, a site used by 200,000 college students to find jobs at places like Microsoft, Uber, The New York Times, Disney, and Google - where Wessel previously worked - says there's one mistake in particular so many job seekers make … and it can be extremely costly.

"I think that people are generally far too modest," she says. "If there's ever a time to brag, it's during your job search and interviews. You need to state your accomplishments and show how your work led to awesome outcomes for your companies. Remember, you need to convince your interviewer that, out of all the applicants the company is considering, you're their best bet."

If you don't take credit for your work and accomplishments, no one is going to give you the benefit of the doubt for being modest, Wessel adds. "And if you don't show proof of your accomplishments, you won't stand out."

The reason this "mistake" is so common, she says, is that a lot of people are good at being "team players," and therefore try to share the credit. "In a lot of cases, this is a great instinct, and while it's obviously important to work well in a team setting, it's also important to convince an employer to hire you, not your entire team.

"I'm not saying you should take credit for an idea that wasn't yours - that would be lying - but if you're the one who executed the idea, then focus on why the execution made the project successful."

People also seem to believe that a hiring manager will do more diligence to see your work outside of the interview, but often, managers don't have time for this, especially if you don't point them in the right direction, Wessel explains. "So if you aren't able to bring your accomplishments to life, you may be forgotten."

She continues: "I also think that a lot of people are simply uncomfortable promoting themselves. I understand that no one wants to come off as arrogant, but you should be able to objectively look at your record of accomplishments and articulate that in a way that helps you sound confident without coming across as boastful."

To avoid making this mistake, Wessel suggests taking 30 minutes before your interview to list all of your career accomplishments. "Find a way to bucket them into themes," she advises. "For example, one project could demonstrate a time when you were faced with hardship, but led your team through it. Or maybe you came up with a marketing idea that was huge for your company. Looking through your record, you should be able to find themes that you can illustrate confidently with examples."

If you have anything physical that you can bring to show off your accomplishments, do it. "If you write blog posts, then print out some of your favorite posts and bring them with you," she says. "It may feel excessive, but this will ensure that the interviewer sees that you mean business."

What you don't want to do is say something like, "I am a rainmaker."

"You'll come off as cocky and arrogant," Wessel explains. "Instead, say something like, 'I'm a confident and hardworking team member, and I'm sure that, if you give me the privilege of joining your company, I can help your company get to the next level.'"

You should always aim for a mix between showing confidence in yourself and deference to the larger goals of the company, she concludes.