When epistemic rationality is counter to instrumental rationality

Epistemic rationality is about knowing the truth. Instrumental rationality is about meeting your goals.

The general case is that the more truth you know, the better you are at meeting your goals (and so instrumental and epistemic rationality are heavily tied to each other), however there exist rare occurrences where this is not the case.

More importantly, there are many times when SPEAKING the truth is counter to your goals.

For an absurd example: Say you are in a room full of angry convicts with knives. It probably is counter to your goal of staying alive and healthy to start proclaiming TRUE but insulting statements.

More realistically, raising children is one example where, if your goal is to raise happy, sane, well-adjusted adults, there are many statements that should NOT be spoken, no matter how true they are.

Examples:

• No, that's a horrid drawing. I can't tell at all what it is. I could do better in 5 seconds. I will probably throw it away as soon as you forget about it.
• Your mom and I just had sex on the living room couch. What's sex? Well...
• Let's learn about the history of torture! Or how about I tell you about factory farming and where your hamburger came from. Or poverty! (if said to a preschooler)

Even if it the cooking and cleaning statement were epistemically true, it is not instrumentally rational to tell this to your child if your goal is to have her grow into an independent adult who can support herself, and does not feel bound by the "traditional" gender roles (which are falling out of favor anyway).

Likewise, if you value having a higher percentage of women on this site, it is not instrumentally rational to make statements such as "You only got upvoted because you're a girl", or "<X> girls aren't as attractive as <Y> girls," EVEN IF you believe that said statements are true.

I highly value truth. But a prime reason I value it is because it allows me to meet my goals. When speaking the truth is harmful to my goals, it is wise to hold my tongue.