Origin
The origin of this proverb is unknown, but its current form is attributed to American humorist Josh Billings who is said to have popularized it in his putative poem “The Kicker” (c. 1870).
Explanation
The person who complains or speaks up most loudly receives the redress or attention which he or she seeks. The loud complainer gets what he wants, gets a reward. That’s how it works in the business world; the departments complaining most noisily get their budgets increased, get their technology upgraded, etc. The ones who plod along silently get more of the same. No one knows they’re hurting, no one knows their needs, so they get nothing. It is said to emphasize that attention is paid to those problems that are made most noticeable. It means that the person who complains aloud is likely to receive most help and sympathy. This proverb means that the most noticeable (or loudest) problems (or people) are the ones most likely to get attention. It is alternately expressed as “The squeaky wheel gets the oil”.
Examples
Becky begged for months to her parents for a new car and she somehow got it. Squeaky wheels get the grease, I guess.
Helen generally insists on a better one and gets it; squeaky wheels get the grease.