Surefire (adjective)

Certain to be successful; guaranteed to work or be effective.

Origin:

Early 20th century: from sure + fire.

Examples:

1. The surefire way to make money in this business is to work hard and be smart.
2. This is a surefire recipe for a great dinner party.
3. He had a surefire plan for getting the promotion he wanted.
4. The surefire way to avoid getting a cold is to wash your hands frequently.
5. This is a surefire method for making perfect pancakes every time.