because you know the stress syllable by looking at the word. take Desert and Dessert, do we say DES-ert or des-ERT. Also in portuguese, at least, I can know which "e" sound [1] each "e" in the word makes by knowing this (well, almost, but not completely, but much better than English.)
[1]: https://en.wikipedia.org/wiki/IPA_vowel_chart_with_audio