Shattering beliefs

No, I don't mean any beliefs of mine that could shatter you. I mean "shattering" as a gerund (go look it up if you don't know what a gerund is). You know something about some people you know that you want to tell them (they're close to you), but telling them would prove disastrous to them, especially if they accept it. Or, you know that their deepest beliefs are based on an edifice of irrationality - which they're unable to see for themselves - and you are loath to destroying their feeling of safety and comfort in those beliefs. What do you do at such times?