expression
a fool's one trick; one who knows little often repeats it
Proverb used to criticize someone who keeps repeating the same limited knowledge or skill, often inappropriately. Literally 'a fool's one memorized thing'.
彼は馬鹿の一つ覚えのように同じ話ばかりする。
He keeps telling the same story like a one-trick pony.
馬鹿の一つ覚えで、何でもその方法で解決しようとする。
Like a fool with one trick, he tries to solve everything with that method.
Another proverb, but about even experts making mistakes, not about limited knowledge.
The phrase literally means 'a fool's one memorized thing', implying that a foolish person clings to the one thing they have learned and repeats it regardless of context. The exact origin is uncertain, but it is a well-established Japanese proverb.