1) The commonest phrase is "no one's perfect." That's also the title of a very funny song by Allan Sherman, in which a beautiful chorus is almost perfect:
2) With regard to work, design, and art, a common saying is "The perfect is the enemy of the good." It means that striving too hard to make something perfect may actually make it worse.
3) I will mention a technical detail of Protestant theology. In Methodism, one of the doctrines is called "the perfectibility of man" or "Christian perfection." This doesn't mean perfection in an ordinary everyday sense, it has to do with the possibility of achieving perfect love of God. However, it is a case where, in a limited sense, some people say that perfection can be attained.