Maybe it's just me getting older but it seems like this has always been true across cultures and history. People like to believe that once they get power, they will act differently than the ones who came before. But in the overwhelming majority of cases, they end up being just like the people they replaced, if not worse.
Every once in a while you get an exception but that's why we remember those people - because they were the exception.
This can cause the actual result of policies to be wildly different from the claimed intended outcome. We’ve seen plenty of examples of this in the past, e.g. claim that you want to make sure everyone will be better off by lowering taxes for the rich (trickle down economics), which of course had the exact opposite effect.
This can be completely malicious, i.e. claim that your proposed policy will have outcome X while knowing it will have outcome Y. It can also be due to flawed ideology, i.e. your policy is based on your idea how the world should work instead of how it actually does work. Or it can be sheer incompetence.
What I would like to see is a system where the goal and the method of achieving it are separated from each other: a democratic technocracy. In this system politicians would only set the intended outcomes, and their relative priorities (in cases where policies would affect different intended outcomes in opposite directions). Then, government workers would decide the policies that would result in the desired outcomes (based on science, evidence based methods, etc.) They would be normal unelected workers subject to performance reviews (did their policies result in the intended outcome) and positions should be completely merit-based.
That way politicians have to be honest about what they want to achieve, people have a clearer idea what they are actually voting for and there is a system in place that will try to achieve those outcomes based on what actually works.