初心忘るべからず (しょしんわするべからず): we were all beginners once; never lose your humility; don't let success get to your head

we were all beginners once; never lose your humility; don't let success get to your head

Do not lose the humility you had as a beginner. Most often said to someone who has started to succeed.

A Japanese proverb (ことわざ)