The toughest call for a leader is judging people. If you do not want to die of stress, you need to know who to give a job to AND not worry yourself into an early grave about whether it will be messed up after you hand over the responsibility. You cannot do it all yourself either; not unless your leadership role is merely honorary. To trust people's sense of responsibility, to trust people's integrity, to trust people's abilities, to trust...you get the picture. You first understand that 'Do you trust me?' IS the most idiotic (OR manipulative) question because it begs the question 'Trust what? Your discretion, your integrity, your loyalty to me, your abilities,...?' AND you have to assess people on what they can be trusted with and what not.
Tiru has this to say about judging people.
Gunam naadi kutramum naadi avatrul migai naadi mikka kolal - Tirukkural
Assess the virtues and faults of each man, and assess him on the basis of the excess of one over the other - Loose Translation
It is a sad fact of life that no person is perfect. We are all a mixture of various virtues and faults. Nor, indeed, is the definition of a virtue and a fault static. I mean, meticulous attention to detail may be a virtue on an assembly line; but has ANYONE lauded it when their medical advance request is being processed for approval? Dotting every 'i' and crossing every 't' while sanctioning money for an emergency operation is unlikely to be considered a virtue. So, yes, circumstances also determine what is a virtue and what a fault.
Tiru is no fan of the sort of leader who seeks perfection. 'One fault and the guy is out' is not his favorite credo. (AND if, indeed, there is any leader who believes in that credo, he will cease to be a leader in jig time unless he is leading an army of drones.) Which does not mean that you should be blind to the faults of the person. Tiru expects you to take on board all his virtues and all his faults; assess whether the virtues outweigh the flaws or not; and THEN assess the person's worth.
You could be a genius and still be considered unworthy as per Tiru's dictum because you are undependable, arrogant and a disruptor. You could be not so intelligent but dependable, meticulous, and dedicated which could make you worthy if you go by Tiru's dictum. So, the assessment of a person is on the balance of his virtues and faults; not on the ABSENCE of faults.
AND, yes, it does not mean that you FORGET the faults even after assessing the person as worthy.You need to keep them in mind while allocating tasks to them. I mean, what's the point in entrusting an R&D job to a person whose strength is meticulously following routine and weakness is in thinking outside the box? OR, for that matter, putting on the assembly line this genius with the attention span of a butterfly?
To lead is to know the worth of people; including a clear idea of what they can be trusted with. And THAT is why you need to know how to judge people.