The idiom jump the gun means a person may have acted too hastily or made a snap decision based on inadequate or partial information. The phrase could be used for an employer who hires the first applicant he or she interviews, for example, or a news organization that projects a winner based only on a handful of election returns. By assuming facts not in evidence, a person can often assume the best or worst case scenario in any situation.
The origin of the idiom can be traced back to the early days of track and field sports. Many running events required the use of a loud, unambiguous starting signal in order to guarantee an equal and fair start for all competitors. Officials originally used a real handgun to signal the start of a race, then later employed a modified "starter's pistol" that used blank cartridges. Any runner who ran out before the shot was charged with a false start and faced disqualification. Runners soon learned to wait for the sound of the starter's pistol and not jump the gun.
In a modern sense, jumping the gun can imply a deliberate attempt to gain an advantage over competitors. An ambitious company with a new product may feel tempted to release it to the public ahead of a competitor's similar product. This may prove to be a wise move because consumers become loyal to the first product on the marked, or it may be unwise because the product has not been fully tested before release. In many cases, a company that releases a product too soon can rightfully be accused of jumping the gun with consumers.
To jump the gun can mean to make a rush to judgment before all the facts are known. Sometimes this kind of anticipatory action can have a positive result, but much of the time someone who jumps the gun eventually makes a wrong or misinformed decision, or takes the wrong set of actions based on inaccurate early information. Quite often, a piece of bad or disturbing news is delivered along with an admonition not to assume the worst until all the facts are in.