Here's why:
* "Distress" is a single word with its own meaning: suffering mental or physical pain.
* The "dis" in "distress" is part of the root word itself and doesn't function as a separate prefix. It's similar to how "dis" is part of "discover," "discuss," and "disarm," not acting as a prefix in these words either.
While prefixes can be helpful in understanding the meanings of words, it's important to recognize that not all words are formed by adding prefixes to existing root words. Sometimes, the root word itself holds the meaning, and understanding the word's history and usage is crucial.