I came across this phrase that I don't get the meaning: the principle of the thing. Here's the sentence that includes this phrase (a questionnaire item):
I have, at times stood in the way of people who were trying to do something, not because it amounted to much, but because of the principle of the thing.
Best Answer
I know a guy who went to small claims court to get out of paying a bill he felt he should not have been obligated to pay. He didn't have to pay the $800 bill, but he paid almost $2000 in legal costs.
Some might have viewed that as a net loss, but he considered it a victory, because of the principle of the thing. In other words, he felt it was more important to not pay the bill than to save the money.
Your quote mentions people who "were trying to do something." That's rather vague, but the idea is that, whatever they tried to do, there's a good chance they wouldn't gain anything personally, yet they persevered anyway, because they felt it was the right thing to do.