A great doctor is great, mostly due to his/her ability to correctly diagnose a medical condition. Once correctly diagnosed, the best treatment or cure is often quite clear. The same goes for managers who are looking to improve the job performance of others. The key is to correctly diagnose the true, underlying reason for the performance issue.
So how best to do that? Ask the person "why?" in various ways, such as... "Why did you miss your deadline?" "What obstacles prevented you from meeting your deadline?" You may get lucky and uncover the true, underlying reason at that early stage. More likely, you will need to probe further. For example, if their response is, "I ran out of time," your probe could be, "Why did you run out of time?" or "What did you prioritise ahead of meeting this deadline?" Continue to probe with "Why" until you are confident you have reached the true, underlying cause.
There is much more to share on the art and power of "Why" that I will share in upcoming blogs.