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.
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.)