Even though everyone doubted him, he insisted that he was right.

insisted 是动词 insist 的过去式，insist 由前缀 in-（表示"加强"）和词根 sist（来自拉丁语，表示"站立"）组成，字面意思是"坚定地站立"，引申为"坚持、坚决主张"。