I was thinking about four different expressions, interestingly different, for the platitude that people shape their consciences to their circumstances.
The most straightforward is the English classic
Who pays the piper calls the tune.
This is the most straightforwardly economical. The boss makes the decisions, and the opinions of the underlings are irrelevant. It says nothing about what those underling opinions might be.
A step more cynical is the old-German proverb
Wes Brot ich ess, des Lied ich Sing. [Whose bread I eat, that’s whose song I sing.]
It has the same general musical theme, suggesting the court jester performing for his master. But the singing, rather than piping, is more intimate, and to my mind suggests a more complete subordination of ones own beliefs to those of the master.
Perhaps the most pessimistic is the saying that Mark Twain claims to have learned as a boy, from a young slave:
You tell me whar a man gits his corn pone, en I’ll tell you what his ‘pinions is.
In other words, as Twain explains, no one can afford to have opinions that interfere with his livelihood. It’s not a matter of dissembling — which is what makes this more pessimistic (but maybe less cynical?) — but rather of naturally adopting the opinions that are a comfortable fit to his circumstances. (Twain’s more cynical version was “It is by the fortune of God that, in this country, we have three benefits: freedom of speech, freedom of thought, and the wisdom never to use either.”)
And then there was the perfection of the corn pone line, the famous dictum of Upton Sinclair,
It is difficult to get a man to understand something, when his salary depends upon his not understanding it.
Here we see the complete identification of master and slave. The slave not only gives voice to his master’s views, he not only comes to accept the master’s views, he has deformed his intellect to the point where any other opinion has become completely incomprehensible to him.