不屈不挠
Stick to one's colours.
Firm and unyielding.
Fight for it tooth and nail.
Hang on by the eyelashes.
Keep one's chin up.
As steady as a rock.

eg：To gain confidence of others for your idea, you have to stick to your colours.

中英俚语俗语来源：汉书·叙传下：“乐昌笃实，不挠不屈。”

同义词：百折不挠 Stick it out.
反义词：俯首就范 Give one's head for the washing.