be blown off course
1. Literally, to be pushed off the route that one is trying to follow, as of a ship in the wind. Captain, do you know where we are? I think we've been blown off course!
2. By extension, to have one's plans interrupted or interfered with. I just don't want your goal of becoming valedictorian to be blown off course by anything—including this new girlfriend of yours.
be blown off course
have your plans disrupted by some circumstance. This phrase is a nautical metaphor: contrary winds turn a sailing ship away from its intended course.