Reading is a skill that can be learnt with good teaching, and practice. Once the rules that apply to reading have been taught and reading has been practiced a number of times then the physical aspect of reading and word recognition should be automatic. The content of what has been read can then be processed, interpreted and comprehended.
However if reading is not automatic then each time a word is viewed it must be thought through and deciphered. This in turn requires increased mental capacity and even then doesn’t necessarily guarantee the word is read correctly. As a result reading is a struggle, slow, inaccurate, and requires a lot of mental effort. This usually results in poor levels of comprehension and tiredness when reading.