He teaches ill, who teaches all.
" This proverb is a little tricky to understand due to its unusual structure. It becomes easier if we change the sentence structure round so that it reads "He who teaches all teaches ill." The word "ill" here means "badly". Therefore, the proverb means that a teacher, who teaches students everything, does not teach very well. A good teacher lets their students discover some things for themselves. • ill (an adverb) means badly