Dos and don'ts are subject to personal style ... some 'exceptions' to the rules will never work, but others work well for individuals.
I, for one, have worn FC shirts without a jacket for years. This means, of course, I also wear them without ties. That makes sense, considering I was wearing FC shirts with jeans in my 20s when this was unheard of.
Was this a "don't"? Perhaps. Nonetheless, my point is that within the confines of my personal style these fashion 'don'ts' became 'dos' and worked very well.
Some don'ts will never transcend, while most dos will work well for anyone. You must be mindful moving in one direction, while the other requires less caution.