The phrase often implies a lack of thought or planning, suggesting impulsiveness. He jumped the gun on the project and now we have to start over.
Pro Tip 2/3
Negative Outcome
Using 'jump the gun' usually points to a negative result due to early action. Jumping the gun led to a misunderstanding with the client.
Pro Tip 3/3
Metaphorical Use
Despite its origin in sports, the phrase is often used metaphorically in different situations. Don't jump the gun and assume they will agree to the deal.