Dishonesty in politics is nothing new. First, lies can hold political systems together. Second, lies can be strategically valuable to achieve their goals. Third, lies can cement the loyalty of subordinates.
It is quiet hard to fool large groups of people for a long period of time.
Psychological literature on persuasion suggests that people can be persuaded to believe in many false things, especially when they have little personal experience or interest in the matter, or explicitly trust the source of the false message.
But it is difficult to get people to keep believing claims that conflict with what they can see with their own eyes, or that conflict with their deep seated identities.
People actively and passively tend to avoid information that contradicts their beliefs or way of thinking. Actively means that they will choose which articles to read, choose to ignore the speech of a politician they do not support, and generally coose to select the information they will consume.
Passively means re-interpreting the information you receive if it runs against your beliefs, judging it or adapting it to match your opinion so that you won’t have to doubt your own thinking.
Lies help ensure the loyalty of subordinates who are forced to repeat them. These kinds of lies need not be credible at all to people outside the regime.
The more incredible a lie is, the more it can credibly signal loyalty to a political leader in conditions of low trust. When a subordinate repeats an obviously ridiculous claim he is degraded, and bound more closely to the leader. This happens in democracies too.