Not every principle herein has to be strictly followed, and even fewer will be universally agreed upon. These are guidelines and nothing more, but they are ones codified over many years of collective experience by the authors of Clean Code.
One more thing: knowing these won’t immediately make you a better software developer, and working with them for many years doesn’t mean you won’t make mistakes. Every piece of code starts as a first draft, like wet clay getting shaped into its final form. Finally, we chisel away the imperfections when we review it with our peers. Don’t beat yourself up for first drafts that need improvement. Beat up the code instead!