A counsel of perfection
Definition 1 of 1
Pro Tip 1/3Ideal but Impractical
Emphasizes how an idea is theoretically perfect, yet not realistic due to life's limitations. 
Eating a perfectly balanced diet for every meal is a counsel of perfection for most people.
Pro Tip 2/3Unattainable Standard
Highlights a standard or expectation that is too high to meet. 
Asking the team to make no mistakes at all is like a counsel of perfection.
Pro Tip 3/3Gentle Criticism
Often used to softly criticize someone's overly optimistic or demanding suggestion. 
Your idea for weekly community clean-ups is a counsel of perfection, given our tight budget.