Projection
A year ago, I wrote Proprioception, where I argued that other people observe you based on your external effects, but you need to measure yourself by your internal compass. Anything else is just giving up your sense of self to forces beyond your control, which is unreliable and dangerous. I've been thinking recently about the link between internal and external perception, so I'd like to take a shot at an important way in which this is reversed.
I don't know if I could commit to never lying, because despite my ideas about truth it seems obvious that there are situations where lying could lead to the best outcome. However, mostly when we talk about lying we assume that same division between internal and external perception. In your mind, you believe the truth. Outside it, people believe the untruth. This division is so fundamental you can use it to test for a developed theory of mind.
"Be yourself" is advice I've dumped on (twice), and justifiably so. But if it's such bad advice, why does it get repeated? Is there any kernel of usefulness hidden in there? I think so, and it's for the simple reason that the internal–external division is not as airtight as it seems. In reality, we imply both ways, and the way we act externally influences how we feel internally. The advice "be yourself", generously interpreted as "act like you're comfortable with yourself", is not so bad. Over time it might come to be true.
In general, I think we must be very careful not to pretend that we act in an external vacuum separate from our internal sense of self. The version of ourselves we project to others is the version of ourselves we see reflected back. The things we say end up being the things we believe. And, while lying to others might sometimes be justified, it so easily leads to the unjustifiable: lying to ourselves.