It probably looks impossible at first. But as you scan through the page, the words seem to materialize. As you continue to scan down the page, you may find that that the task is easy. Then, when you shift your gaze back up to the top, the message that was obscured seems to pop out.
When reading, the brain naturally scans for patterns and whole words. If you focus on individual characters, then it is clear that the print combines numerals and letters in a way that does not make sense. Certainly it is not a set of phonetic representations that anyone could “sound out.”
But when the mind shifts to a focus on whole words, the pattern becomes obvious. The numerals simply stand in for similar but familiar letters.
The number 7 is close enough to T; S can be represented by the more angular 5; a 1 easily substitutes for the letter I. Even the reversal inherent in using 3 as a stand-in for E in the word “R3AD” and the phrase “B3 PROUD” is easily reconciled.
This it the same process that allows us to read a variety of fonts, including ornate calligraphy scripts with a variety of letter forms. Our brain is wired to focus on the pattern and not the individual character.
This is why it is important that reading be taught as a process of whole word pattern recognition. Phonetics provides an important clue to deciphering unfamiliar words, but the brain relies primarily on the visual system in developing automatic word recognition skills.