The truth becomes easier to hear when it is not wrapped in humiliation.

Criticism wrapped in humiliation cannot be heard, because the person is busy managing the shame rather than considering the substance. The point may be entirely correct and it will be defended against, resented, and eventually discarded along with whoever delivered it.

Separate the message from the diminishment. Say what happened and what you would like, without the commentary about what it says about them. It is not softer in content, only in what it does to the person, and it dramatically raises the chance of the truth actually landing.