stick to one's guns

verb2

1. •
   (figurative) To maintain one’s position or viewpoint when faced with opposition.

   • Ronald had stuck to his guns and refused me to the last. — 1898
2. •
   (old-fashioned) Of a gunner, to persist in faithfully attending to cannons while under fire.

adjective1

1. •
   (informal) Refusing to compromise, change one's mind, or abandon one's beliefs despite opposition or criticism; steadfast, resolute.

   • The stick-to-your-guns approach had made Silky Soul both a commercial and artistic triumph, and it's also a major asset on Back to Basics. — 1993