I like the Werner Herzog take on truth, that facts are the domain of accountants and phone books. Of course, he's talking about making movies and 'documentaries' and not specifically about how to interact with other humans.

When dealing with people I don't care about, I have no problem lying in many cases. For example, if I'm taking a day off of work and I don't think it's anyone business why. In that instance, and many similar ones, the lie isn't necessarily made in order to deceive, but rather to avoid an unnecessary conversation. On the other hand, nefarious lies never feel good, even in cases when telling the truth would be perhaps more harmful. Anyone who has ever been betrayed by a trusted loved one knows the hurt that a below board action and the subsequent lie to cover it up can cause. I've been on both sides of it, and it's certainly not enjoyable in any way.

But my short answer to your question is that the question itself is kind of nonsense. We can't tell the truth all the time; it's not just impractical, but rather impossible. Should we be fully expected to answer honestly when asked, "What are you thinking about?" I suppose "none of your business" is an appropriate answer, but seems a bit off putting and unsociable.

There's no moral high ground in always telling the truth. There is, however, moral high ground in treating people with respect and dignity, especially loved ones, and often times telling lies becomes the vehicle through which we violate that principle.