In sales and marketing, the job becomes orders of magnitude easier if the product is actually as good as promised. When your product is lower quality than the competition, advertising it is possible but difficult (and I would say ethically questionable) and you're not going to succeed with everyone.
It's the same with "convincing someone of something". The job becomes many times easier if the thing you're trying to persuade them of is actually true. If it's true, you can use plain facts and clear logic. If the thing you're trying to convince them of is false, you'll have to make increasingly more effort and will see a lower success rate. You'll also have to use dishonest tactics, like changing the meanings of words and declaring certain lines of argument taboo or unacceptable in polite society (i.e. political correctness).
A corollary is that, if you (from your POV) find it increasingly difficult to persuade People of Things, it might be worth considering the possiblility of whether those Things might in fact be wrong, rather than jumping to the conclusion that those People are deficient. You should at least consider it, and maybe take some time for personal study of the issues and arguments before redoubling your advertising budget.