Pwno said: I find it hard to imagine a time where truth-seeking is incompatible with acting rationally (the way I defined it). Can anyone think of an example?

The classic example would invoke the placebo effect. Believing that medical care is likely to be successful can actually make it more successful; believing that it is likely to fail might vitiate the placebo effect. So, if you are taking a treatment with the goal of getting better, and that treatment is not very good (but it is the best available option), then it is better from a rationalist goal-seeking perspective to have an incorrectly high assessment of the treatment's possibility of success.

This generalizes more broadly to other areas of life where confidence is key. When dating, or going to a job interview, confidence can sometimes make the difference between success and failure. So it can pay, in such scenarios, to be wrong (so long as you are wrong in the right way).

It turns out that we are, in fact, generally optimized to make precisely this mistake. Far more people think they are above average in most domains than hold the opposite view. Likewise, people regularly place a high degree of trust in treatments with a very low probability of success, and we have many social mechanisms that try and encourage such behavior. It might be "irrational" under your usage to try and help these people form more accurate beliefs.