insistence
Firm, repeated demands for something without giving up.
Insistence is the act of demanding something firmly and repeatedly, refusing to give up or back down. When you show insistence, you keep pushing for what you want or believe, even when others resist or ignore you.
If your little brother shows insistence on staying up past his bedtime, he keeps arguing and pleading no matter how many times your parents say no. A teacher might speak with insistence when reminding students to show their work on math problems, bringing it up again and again because she knows it matters. When a detective questions a suspect with insistence, she keeps asking the same questions from different angles, determined to get real answers.
The word carries a sense of determination and stubbornness mixed together. Sometimes insistence is admirable: a scientist's insistence on careful measurement leads to accurate results. Other times it can be annoying or even counterproductive: insisting you're right during an argument might make others stop listening, even if you have a good point.
The related word insistent describes someone who shows this quality. An insistent knock on the door is one that keeps going, demanding attention. An insistent person doesn't give up easily, which can be either a strength or a weakness depending on the situation and how they express it.