Yesterday I was asking about credibility. The common advice on credibility is that consistency and attention to detail are a big part of establishing credibility. It has been observed that associating with credible people helps and that making distinctions is important. It has also been suggested that smoothness and personal beauty are more important than people would like to admit.
In addition, though, I would like to suggest that proportion is an underrated component of credibility. If you can consistently separate the big stuff from the small stuff, that is more credible than if you get the big stuff and the small stuff confused, or if you mix them together in an attempt to confuse others. At the other extreme, people who react to every event as if they are all equally big or little give the impression that they are not paying attention — and attention, it seems to me, is where credibility starts.