Dt 27:26 says "Cursed be he that confirmeth not
all the words of this law to do them." Which is why Paul says in Gal 3:10 "For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them."
Why? Because as you hinted earlier, no human can fulfill the law perfectly. Without a Savior, everyone under the law is cursed.