Certain of my early books I can't bear to read because the italics leap out and poke me in the eyeballs.
We all do it. Overuse of emphasis is one of the major pitfalls - too many adverbs, strings of adjectives, italics. And heaven help us all with the dreaded exclamation mark.
I'm still paranoid about them, even though it's a good twenty-five years or more since an editor remarked - with unwarranted sarcasm in my view - on my manuscript littered with exclamation marks: "I assume it is meant to be funny."
I still regard the things with horror - I take them all out, put some back in, scream blue murder and take them out again. And finally argue the toss with myself for every one I desperately want to keep.
The truth is we over-emphasise because we are not convinced that simple prose will put our point across. We don't believe the reader will get it if we don't really truly force them to understand!!!
We need to trust the reader. We need to grant them intelligence enough to be able to read between the lines. Reading, unlike film or TV, invites participation from the audience. The reader wants to use their creative imagination too. Whack them over the head with it and they don't get the chance.
Scatter the whole text with emphases and they all lose force. Emphasise sparingly and each one will have a stronger effect.