What are economists referring to when they say choosing is refusing

Considering the case of the two health clinics above, why do you think that trouble was brewing? there was serious competition for tech jobs at the downtown clinic. the new technology at the uptown clinic was too difficult for the staff to understand. the doctors pitted the staff of one clinic against the staff at other clinic. the staff at the downtown clinic saw that their colleagues at the uptown clinic were treated better and had more opportunity.