fixed idea

基本解释

As for Marius, as he allowed them to dress his wounds and care for him, he had but one fixed idea: Cosette.
至于马吕斯，他任凭别人替他包伤，护理，心里牢牢地只有一个念头：珂赛特。
This system tends to produce a tough, rather brutal, stupid, unscrupulous class, with a fixed idea that all enjoyment consists in undetected sinning;
这套体系企图创造一个充满暴力，而残忍的、愚昧的、肆无忌惮的阶级，形成了一套固定的想法，即一切享受都包含不易觉察的罪恶；
It is your fixed idea that you must be something or other that blinds you.
是你那要成为某些或其他东西这种固执的想法将自己蒙蔽。

They bring with them a fixed idea of what a university is all about, and are unexcited by what they consider their chancellor's unglamorous goal.
ECONOMIST: Higher learning and the middle classes
Not least of which is the question of original sin, a tradition that seems harder and harder to reconcile with what science is telling us about human origins, because it presupposes a fixed idea of human nature.
FORBES: Paleogenomics Will Not Lead to Gatacca--If We're Vigilant

an idea, esp one of an obsessional nature, that is persistently maintained and not subject to change (See also foreign: ide fixe)