I believe that there are three requirements for any situation to warrant tochacha:
1) The person giving tochacha has to genuinely care about the wellbeing and situation of the one he is giving it to, and the person receiving it has to both know that, and fully reciprocate that feeling. If he doesn’t then the person will not receive it properly, let alone at all, as he will feel the person has no business rebuking him and is a mere annoyance.
2) There has to be a safe environment when it is given. This is especially important when it is an authority figure giving the tochacha. If the receiver doesn’t feel safe, if he thinks he would get in some trouble or if he doesn’t listen the relationship he has will go down the drain, his primary focus will be ensuring that those things don’t happen, not the tochacha, and he will pay the message no attention.
3) The person giving tochacha has to know the full situation of the person and the general mindset that person has. Without this, it could lead to extremely embarrassing mistakes, could cause the person to take offense, and the person giving it simply won’t know if other factors are at play, thereby rendering his mussar irrelevant and therefore hurtful.