This may seem a strange claim.
You have a grant or your department has a position. You fail to attract the quality of candidates you hoped, particularly after some attrition as the better candidates accepted positions elsewhere. But, you should hire someone. Otherwise the grant will go to waste, you will lose the position, or at least everything will be delayed for a year. Voices (both internal and external) will say you should just hire someone.
No! This can be a mistake.
Sometimes there will be people (whether graduate students or faculty members) who will turn out to be a net drain on your resources (not just money but time, energy, and lab consumables) and relationships (harmonious research group or departmental). Be particularly wary of people who have a history of not getting along with others. You may wish you never hired them.
Fortunately, I have never experienced this first hand. However, I have seen disasters happen. Sometimes for this reason I have postponed hiring someone. Once I never filled a funded Ph.D position since I just could not find anyone suitable.
No candidate is perfect. Be willing to compromise your hopes and expectations. But, never hire anyone out of desperation.
Cartoon is by Kerry Soper