When we take a lesson with someone we want them to tell us the 'truth' about our playing and what we need to work on to improve. The problem can come when the teacher is harsh or not sensitive in who they are dealing with. It has been my experience over 47 years of working in the private lesson situation that people by majority respond better when the area they need improvement on is put across with care and humanity. Is this 'sugar coating' the truth? Not to me it isn't, especially if you are considering the age of the person and the intensity of their declared pursuit.
Working with people who are not totally committed in wanting to pursue music for their career do not need to have it said to them "you sound awful." The teacher, if wanting to have a relationship with the student in a musical way, should attempt to find a 'doorway' in the person that can lead them to inspiration and insight. The student, for example, might love sports. In this case you can make lots of references and find connections to their playing with sports analogies that can help them make the link to music and playing their instrument. This approach can also help with students who are very serious in wanting to make a career in music too. Instead of necessarily saying "you sound awful" (which in a lot of circumstances is a short- cut statement and does not get to the root of the problem), the teacher could ask "what were you thinking about when you played that?" Or, "how were you feeling when you played that?" That will reveal much more and cut to the chase much quicker. If it is a case where a student repeatedly over several lessons is not sounding well and if it is clear the cause is lack of enough practicing, this needs to be addressed directly. Some teachers might just kick someone out of the room for wasting their time. For me, I will usually sit the student down and ask, "what's going on, are you alright? I have noticed a trend over the last few weeks."
Truth is a HUGE subject and not everyone sees it the same. What is a nice sound to one person could be too heavy and 'dark' to another. So how can we help someone find their 'true' sound? Is there such a thing? Perhaps the question in this case should be: does it sound natural? Now here is a truth for me: I have discovered that we all have biases and this can get in the way of accepting variety or variations in sound style, articulation or musicianship and yes, even in pitch and rhythm.
Let's look at this in this format:
Obvious Truth Not So Obvious Truth
All need air to play The usage of it is not the same for all
All need energy to play The origin of the energy is not the same for all
All have a reason to play The reason is not the same for all
One can certainly add to this list if one would like to. It is a good exercise because it will get a teacher more in tune with the importance of looking for deeper truths and reasons which will aid in finding an approach that will work for a particular student. It will also make the interested teacher aware of his or her biases and how they affect their teaching.
Once you find the reason why someone plays, it can change your whole approach to them.
Here is a ponder:
There are major truths and minor truths. Causes and symptoms. Both are truths but one is more major and is the cause of the other. Go for the root cause. But be mindful in your approach. Most people cannot accept the whole truth at once. Truth is a powerful sword and can cause damage if not approached with care, patience and understanding. Humanity is the key.