my advice for mate selection for any person is that while it is good to have things in common like both being rationalists it is more important to have values that complement each other. So if you focus a lot on theory then someone who is more practical, might be better for, if your indecisive then someone who is a bit impulsive could be good for you.
If you are good at math and bad at English then a good match for you might be someone who is bad at math and good at English. So maybe the best match for a rationalist isn’t another rationalist.
My view of the relationship between honesty and rationality is similar to taw’s theory ‘enhanced reality’ in his comment on this page, but I would think of it as a ‘augmented reality theory’, I don’t think we are designed to lie just that the truth is normally very complex, and we are designed to simplify.
I think there are two basic factors that limit honesty Language, and the way the human mind works.
LANGUAGE
Even a person who is trying to tell the truth and be honest is always going to have language problems, it’s important to remember that new words are still being created all the time and it is impossible for one person to know them all, and we have to learn them, and even when two people are speaking the same language there is still going to be miss interpretations. before I found this site I had a lot of ideas in my head but wouldn’t have been able to describe them or write them down clearly because I didn’t know what words to use or the way to use the words, to express what I meant.
So for example I am doing a IT degree and I have been asked by my wife before what are you doing when I have been sitting at the computer writing, Some times I give her an accurate and honest answer like “I’m trying to fix a problem in the back propagation learning function in the code for my neural net assignment.” and she just looks at me funny, because she doesn’t know what half those words mean, and other times I just tell I’m programming or doing an assignment, even through a lot of the time I’m not exactly programming or doing an assignment I might be installing software I need so I can program or reading information so I can learn how to do an assignment. But giving a long more accurate answer would actually tell her less than giving a short slightly inaccurate one.
The Way The Mind Works
The other problem with honesty and the truth I think is the human mind, because peoples minds work by building associative links and over time the more these links in the mind are used the stronger they become it becomes impossible to change them instantly, and so to change them will take time. For example I have christian friends that if I was to sit down and argue with them that God doesn’t exist would be pointless I would most likely just get a circular argument and even if I did provide them with the evidence they wouldn’t accept it. The best thing can do is understand where they are at and slowly introduce new concepts. this isn’t just something that happens with people who are religious if you look at a lot of the scientific break through s they where not instantly accepted because they where logical and gave the correct answers the ideas where slowly accepted over time.
So I think it is sometimes important to lie when the lie is a part of a bigger process of getting to the truth.