This is a great tool in my experience as well. I would add that it is not only useful to phrase your criticism as a question, it is also useful to try to think

This is a great tool in my experience as well. I would add that it is not only useful to phrase your criticism as a question, it is also useful to try to think through the possible answers, because there may be a logical one. Doing this can save a lot of embarrassment as well; it can be a rotten feeling to give a harsh assertive criticism, only to find out that you were completely incorrect (not that has ever happened to me!).