"Hold your horses" is an idiomatic expression that is often employed as a colorful admonishment to exercise a degree of patience, or to avoid acting rashly. The imagery of the English saying has to do with the need to rein in horses that are somewhat jittery and are about to run away. It is not unusual for this phrase to be said when there is a perception that someone is about to act without thinking the process through or is about to respond to a situation without giving the response a reasonable amount of thought in advance.
The origins of the phrase hold your horses is often accredited to the first half of the 19th century, in the American South or West. One school of thought attributes the origin to circa 1844 in New Orleans, tracing the phrase back to the slight different “hold your hosses” that appeared in some print publications of the day. "Hoss" was a relatively well established slang term for "horse" during this era, and tended to be used in frontier areas as well as established towns and communities in the Deep South. Owing to migrations from the South through the middle and latter part of the 19th century, people took this and other colorful sayings along with them, spreading the usage to other areas of the country.
There is also some difference of opinion as to when the phrase morphed into "hold your horses." One idea is that the advent of talking motion pictures helped to popularize the phrase, using the more proper "horses" rather than the slang term "hosses." In any event, the usage throughout the United States was well established by the middle of the 20th century, and continues to be an easily recognized idiom today.
Parents, teachers, employers and loved ones are all likely to admonish someone using this idiom from time to time, as well as be on the receiving end. An individual may be counseled to "hold your horses" when tempted to respond in anger to some real or imagined slight, when about to make a purchase that would likely throw the household budget into disarray, or when thinking of accepting a job without fully understanding the responsibilities and benefits associated with the position. Typically, the idea behind telling a loved one to hold your horses means to step back from the situation, take a more comprehensive look at all relevant factors, and regain some degree of objectivity before determining how to proceed.