Teaching is a procedural method to impart knowledge from one to another, knowledge can be on any kind or any type, it is procedural because step by step only you can build profound knowledge in someone who is willing to learn not only it develops more curiosity for knowledge being imparted to him/her but also leads to wisdom hence the basic motive of teaching is achieved which is to make sure the knowledge imparted is used in right direction and that only be achieved by wisdom attained by the person using it. As we know Rome was not build in a day and so is not the knowledge, it acquires lots of determination, time and practice and what if all the negative thoughts that keeps you from attaining what your goals overcome all your abilities, what if the only thing that stands between you and your goal is your very own negative thoughts. The inability to utilize all your assets , your potential leads you to the conversion of your greatest fear into reality thus negative thoughts and praise do no good to one it only helps to further degrade yourself and put one step behind from where you started. So no nobody who want to teach will demoralize his/her student to hinder his progress. The praising for ones achievements leads to motivation that results in more dedication and devotion to achieve the goal, the feeling of being near to your dream and goals accelerate your speed and growth.
On the other hand we know excessive of anything is bad everything should be in balance, to avoid the undesired outcome. A lot of boasting may lead to development of overconfidence that separates the path of you and you desires without a slightest hint to yourself. Everything has its pros and cons and hence praising positive too have some but only if not implemented correctly. A dreamer should dream to achieve but should be aware of reality in order to achieve his dreams, knowing his/her flaws makes it easier to rectify them but no constant critics help the only way that can make you work is realizing your drawbacks in appropriate way and with a positive way of overcoming it.