We've all experienced the disappointment of applying for a job, interviewing--and maybe even making it to a second or third interview--and then not getting hired. Sometimes we feel so certain that we got the job that we're left surprised and confused as to why the offer went to someone else.

Was it something the HR manager saw that we posted years ago on social media, or did we drop the ball with our résumé or LinkedIn profile, or maybe we just had an off day at the interview?

Wendy Burbridge, a seasoned HR professional who specializes in talent acquisition, recently wrote a great book titled 30 Reasons You Didn't Get Hired. In this book, Wendy reveals 30 of the most common reasons why people get turned down for a job, and how you can avoid making the same mistakes.

Here are seven possible reasons you didn't get hired--if you want to see the other 23, be sure to check out Wendy's book.

1. You didn't do your homework

It's incredibly important to know everything you can possibly know about the company you're hoping to work for before you interview for a job there. When you can tell the interviewer what the company does, and how you can bring value to what the company does, then you give yourself a tremendous edge over other applicants.

2. You don't see your résumé as a fierce marketing tool

Says Wendy, "Your No. 1 most valuable selling tool as a candidate is your résumé. If you aren't looking at your résumé like a fierce piece of marketing collateral, then you are doing yourself a huge disservice." Not only that, but you probably aren't going to get that job you want.

3. You missed the pitch

Some job hunters forget that they are salespeople, but instead of selling a product or service, they're selling themselves to a prospective employer. Anyone in sales knows that there are two fundamental rules: solve the problem, and ask for the business. Asking for the business is making the pitch. After you've dazzled your prospective boss with your amazing skills and experience, don't wrap an interview without asking for the job. Be confident and sincere when you make your pitch.

4. No woo

Interviewers want to be wooed--you need to do something to get them on your side. According to Wendy, "What I like is when people make my job easy, and the more woo they provide, the easier my job. So the proof, in this instance, can range from letters of recommendation to awards, prizes, and recognitions, certificates of achievements, and so on. But the best woo by far is when candidates go the extra mile: create a webpage for their application; create a magazine as their résumé submission; attach articles they've written, published, or posted on their blog or others about relevant events related to their field of practice."

5. You don't see failing as awesome

Not getting hired doesn't mean you're a failure, it means that the opportunity or the company wasn't the right one for you. Get back up on that horse and try again.

6. Underselling

Many of us are afraid to promote our accomplishments, thinking it will make us appear to be boastful or arrogant. When you're in a job interview, that's the exact time when you need to be as confident as you possibly can be and sell your accomplishments. Don't be shy!

7. You're desperate!

No one wants to hire a job applicant who comes across as desperate for the position. It's OK--even advisable--to be hungry for the job. Hungry is good. Desperate, not so much.