Answer:
The phrase "as we all know" should generally be avoided in formal writing because it can be seen as presumptuous and exclusionary.
Step-by-step explanation:
Not everyone may have the same level of knowledge or familiarity with the topic being discussed, and using this phrase can make those who do not feel left out or uneducated.
Furthermore, in formal writing, it is generally expected that the writer will provide evidence and support for their claims, rather than relying on the assumption that the reader already knows something. Using phrases like "as we all know" can make it seem like the writer is trying to skip over the important step of providing evidence and justification for their argument.
Overall, it is best to avoid using phrases like "as we all know" and instead focus on providing clear, well-supported arguments that are accessible to a wide range of readers.