It’s called best laid plans.

The idiom “the best-laid plans” conveys the inevitability of unpredicted problems or changes disrupting even the most carefully organized plans or projects. If you reference “the best laid plans,” you’re acknowledging that, despite meticulous planning, things might not proceed as expected.

The demand for perfection is always a misunderstanding

 “The demand for perfection is always a misunderstanding of the ends of art. Imperfection is in some sort essential to all that we know of life in a mortal body, that is to say of a state of progress and change. Nothing that lives is, or can be, rigidly perfect; part of it is decaying, part nascent. The foxglove blossom-a third part bud, a third past full bloom, -is a type of the life of this world. And in all things that live there are certain irregularities and deficiencies which are not only signs of life but sources of beauty.”

-John Ruskin.