Solution 2 The two main Sector Lines of interest here are those shown above the weak 3 stone Black group in the lower center, and both are White’s.
The longer Sector Line encloses much more territory, of course, but its upper anchor point stone is so distant from the target Black group that if it were the only Sector Line operative here Black could safely ignore it for the moment, if that was globally appropriate.
But the shorter White Sector Line’s right anchor stone is close enough that Black must pay attention!