When you want to criticize someone you know and care for, paradoxically it may be kinder to do this in writing . Doing this face to face allows you to observe their body language , but the problem is that people will often start becoming defensive and switch off when they hear anything negative.
On the other hand, if you write stuff down , you have to be a lot more thoughtful , and you don’t allow your emotions to get the better of you . It also gives them time to absorb what you have to say, and perhaps they will realise that your intention is good , so they can improve . The goal is to avoid getting into a slanging match !