Basically this phrase means that it's impossible to impose conscience on any given subject, on anyone when said person is motivated otherwise, be it an economic, social, or emotional motivation.
For example, politicians, they will engage in mental gymnastics and dance around a subject indefinitely. One might think that politicians are stupid because of their inability to answer a straightforward question. But in fact politicians know what side their bread is buttered on and to this end thy'll never (intentionally) allow themselves to be pinned down, they´ll fain ignorance before admitting a mistake, that is until it's in their best interest to flip-flop on any given subject.
Another example could be someone that works for a company that does more harm than good, for example, someone that works for a cigarette company, when confronted they will never straight out say that their product kills people, and I'm not talking about CEO's or some one giving a press conference, I'm talking about any one from a forklift driver to a sales associate. Who would knowingly hinder their and their family's future survival?
