knock on (one's) door

knock on (one's) door

To present (itself) to one as a possibility or (usually desirable) opportunity in the near future, especially temporarily. It was hard leaving my parents and all my friends from high school, but when an opportunity to attend school in Europe knocked on my door, I knew I had to seize the chance. What would you do if the chance to make half a million dollars was suddenly knocking on your door?
See also: door, knock, on