Why do we sometimes miss our spelling mistakes?

Sometimes, we start writing or typing and we feel ourselves forced to confirm a word in the dictionary. In other occasions, we just type, read through and hand the projects in, without noticing our job had a bunch of spelling mistakes that will make the overall impression of our work fall dramatically if detected. Have you ever wondered why we sometimes miss our own spelling mistakes?

Actually, it is because of our brains. To decode a word —that is, to read it—, our brain pays attention to the first and last letter of the word above the rest in the group. Thus, it is easy for us to idenfity spelling mistakes at the beginning or the end of a word. In the middle, we tend to just overlook it.

By the way, did you see the mistake in the word 'identify' in the previous paragraph?

Knowledge + Why?