Despite the fact that it requires patience, one should not work oneself up into a frenzy but keep at it.

keep 是动词，意思是"保持、继续"。 at 是介词，在这里与 keep 搭配使用，表示"持续做某事"。 keep at it 是一个固定短语，意思是"坚持不懈、继续努力"，强调持续不断地做某事。