Are you smarter than a first grader?
Why don't you catch the double the right away, when a young child most likely would? It has to do with your brain's experience level at reading. An inexperienced or learning reader would almost surely see the extra the because new readers tend to read a phrase word by word, taking in every syllable as a discrete chunk of information. With that approach, catching the extra the would occur. However, experienced readers take in phrases and sentences in groups. We also extract information from context and have strong expectations about which words should appear where. So it's not as easy to catch an unexpected, anomalous extra word on a different line. Since our brains are not expecting there to be two instances of the word "the" in a row, when we process the phrase as a whole, our brains ignore it.