GF has been working at a place for around 5 years. After 4 years she was only making $15 an hour. Last year when her yearly review was coming up she was really nervous because she knew that she wasn't making enough money. Her work usually gives reasons why they could only give a 75 cent raise unless you were really good you would get a dollar. She knew that wasn't going to be enough to pay all of her bills. After a lot of convincing I finally got her to stand up for herself in her review.
This was very much out of her comfort zone.
When her boss tried to give her the $1 raise because she was one of the better employees, she told her boss while shaking “if I'm only getting a $1 raise I don't think I'm going to be able to afford to work her anymore because that won't cover my bills.” Her boss was quiet for a bit and then asked her how much she would need to make to cover her bills. She told her at least $20 an hour, a $5 raise. Boss told her give them some time and about a week later she approved the raise.
She just had this years yearly review. They tried to give her a 75 cent raise talking about how big her raise was last year. This time she very confidently to told them that she needed $2 or it wasn't going to work for her. After some grumbling they agreed again to her raise. She has gone from $15 an hour to $22 in a little over a year. That's almost a 50% increase.
Her friend that has been working there longer than her got a 75 cent raise this year and a 75 cent raise last year. She is making $17 an hour for doing the same job as my GF and has been there 1 1/2 years longer. Her friend said that she is too scared to ask for more money in her reviews.
Two different people, doing roughly the same job and one making 30% more with less time on the job just because she asked for it. Not every situation will work out like this but if you never ask you won't ever know.