Out of left field
The more you have a clear plan of action, a trajectory you are trying to follow, the more you are able to see what is in fact coming “out of left field”.
Makes sense. Firmly understanding what is part of the plan, on the trajectory, exposes everything that is not
Unexpected events are sometimes surprisingly welcome, even fortunate. And at other times they present obstacles which we have not anticipated, and which can be utterly frustrating.