Why do users have a tendency to miss things written in big bold/colored letters?

So, I've noticed this quite a lot. Almost every time something is emphasized (be it in an email, website, paper, etc.) with big, bold and red-colored letters, it most likely will not be read by people, whereas the objective is the complete opposite.

Why is that so? I feel this has something to do with the fact that we are looking for some particular thing and we assume it's not in that big fat bunch of text, but it also seems a bit far-fetched.

Any explanation to this? Are there better ways to handle important information?