Some of us don't bother asking for things because we don't think it will make much of a difference. If you're afraid to speak up because you don't think you're terribly persuasive, you're probably not giving yourself enough credit.
Harvard Business Review's Vanessa K. Bohn describes how she and another researcher experimented with the power of persuasiveness:
First, we asked each research participant to estimate how many people he or she would need to approach before someone agreed to fill out a questionnaire, make a donation to a charity, or let the participant borrow a cell phone.
Later, when the participants went out and made these very requests, strangers turned out to be twice as likely to say "yes" as the participants had expected. When they returned to the lab, many participants expressed surprise at how willing people were to go along with their requests. (In a separate set of studies, I found that the same holds true even when people ask others to engage in unethical behaviours, such as vandalizing a library book.)
It's one experiment, but the idea is it truly can't hurt to ask, because getting what you want is probably more likely than you think.
Bohn says social pressure is more powerful than people often realise, and this power comes in handy in the workplace. She argues that companies emphasise strict rules and official titles, and, as a result, employees assume their own influence is limited and dependent on their role or title. Thus, they don't ask for stuff.
Her argument reminds me of an article I read about ways employers discourage negotiating. Often, an employer will make it seem like negotiating salary isn't even an option. I told a friend about the article when he was applying for a new gig that fit the bill. He decided to ask for a higher rate, despite the fact that it wasn't encouraged. He didn't get the higher rate, but the company instead offered him a series of perks that weren't even mentioned before.
The rest of Bohn's article is worth the read. Check it out at the link below.