One of the most interesting facts I ever learned was that a large part of the gender wage gap (women make less than men for doing the same job) comes down to a single factor: Women are far less likely than men to negotiate their salaries.
If you're interested in learning more about this, I highly recommend Linda Babcock and Sara Laschever's two books on the subject, Women Don't Ask and Ask for It. The first book documents the negotiating discrepancy and the negative consequences of not negotiating, while the second one offers strategies and stories that go beyond salary negotiations, about people who were able to get something they wanted simply by realizing they could ask for it.
(In case you're wondering, neither these authors nor I think that gender discrimination is a myth. But which factor can you control in your own job search: Tackling a large, embedded, structural bias, or choosing whether to negotiate your own salary?)
At my first job out of college, I didn't even try to negotiate my salary. It was in the ballpark of what I had roughly imagined my "first job out of college starting salary" should be, so I took it. I hadn't done any sort of research about what that specific job should pay someone with my experience, skills, and credentials.
Then I read Ask for It and learned that I wasn't going to scare off an employer by negotiating. In the jobs I've had since, even when a hiring manager was not able to get me the salary I wanted, they never acted like it was weird that I was negotiating or that they regretted offering me the position. They offered me the job because they thought I was a top candidate, and it made sense that a top candidate would want to be compensated fairly.
In one case, I was able to increase my annual salary $3,000 in a 5-minute phone conversation. If I'd been too afraid to ask, that never would have happened.
You may not get the salary you want if you ask for it, but you definitely won't get it if you don't ask for it.