Sentence:  Over a relatively short period of time , usually about four to twelve weeks , the worker must be able to <WSD>shift</WSD> the focus , back and forth , between immediate external stressful exigencies ( `` precipitating stress '' ) and the key , emotionally relevant issues ( `` underlying problem '' ) which are , often in a dramatic preconscious breakthrough , reactivated by the crisis situation , and hence once again amenable to resolution . 
Meaning of the word marked with <WSD> tags:  make a shift in or exchange of; then we switched"