Personally I say "I don't know" when I don't know. I also try not to express my opinion in absolutes – I tend to tell that "I think that...", "I believe that",

Personally I say "I don't know" when I don't know. I also try not to express my opinion in absolutes – I tend to tell that "I think that...", "I believe that", "as far as I know", etc. It is, in a way, a philosophical position – I am aware that I do not know about many things, that someone may be more expert in a given field than me. So, I am trying to keep an open mind, be open to discussion, and not impose my own opinion on others just because I feel that I am right. I have been living by these principles for years and I feel good. However, I would not advise anyone to take similar stance. It depends on the company culture, probably it differs from country to country too... Still, from my experience, it may hurt you career. In most places where I worked, that kind of behavior was perceived as a weakness. Hell, I remember being told that I will not become a manager, because there is no place for "don't know". But it was quite toxic workplace anyway.