You can just say ‘no challenge is simple’ instead of sounding like an ill-conceived example sentence from Intro to Semantics.
I see that it literally seems to mean that no challenge is simple but I can't help but wonder whether it might be understood to mean not every challenge is simple. (Which would be a more reasonable sentence.)
Why do you need both ‘every’ and ‘all’? The Tips & Notes sure don’t explain it.
All these unexplained inclusion of 'đều', where it seems redundant to an English speaker.
Please explain the use of dều.