I hate it when I'm deep in a book and get interrupted. Woe betide you if you phone trying to sell me double glazing or PPI insurance protection. But then, what to do about the author who constantly interrupts me reading their story?
Anything that interrupts my reading focus is an interruption which is why you need to edit and edit and edit to make sure that there's nothing to stop the text flowing. This is where beta readers come in, friends who will read and note any places where they had a hiccup in the reading experience. Hopefully they'll pick up things like this, seen in last Saturday's Times:
"Freddie Max Wright was born on November 18, 2011. Freddie was born with a full head of hair weighing 8lb 3oz."
That's some hair! If you were reading it in a story you might blink, smile, and then carry on but even that momentary loss of focus might be enough to break your commitment to the story. If there are repeated mistakes, then the reader will give up. That's why it's so important to make sure the text is as clean as you can make it. No typos, no grammatical glitches and nothing to stand in the way between your text and the reader.