By chance I was able to land a job in a specific area within finance, despite not having a degree in the field. The job was very basic at first, which was reflected in my salary, but I didn't mind as I was just starting out and learning a lot.
Fast forward 2 years, I'm handling a lot of daily tasks, data-export and analyzing and thought it was time for a raise. I spoke to my coworkers and realized that most were making 20-25% more than me, despite us doing the exact same work.
I spoke to my boss and he agreed that a raise was in order – 5%. He told me HR wouldn't allow for more as I was still “new and had no specific education in the field”. (For this specific field, there is no official education). I tried to negotiate, but to no avail, “His hands were tied”.
For unrelated reasons my boss found a new job and my coworker (who'd been working 6 months longer than me) applied for the position and got it. She had been open about her starting salary from the start and called me into the office for a 1-1 talk. After we discussed my talk with our former boss, she talked to HR and our Head of Department which resulted in a 20% raise – apparently my old boss had never spoken to HR.
Discuss your salary with coworkers – Know your worth!