I was brought-up on the idea that power corrupts; and that absolute power corrupts absolutely (paraphrasing historian Lord Acton).
This seemed like the lesson of history - for example the Claudius novels by Robert Graves is largely a litany of exactly such corruption, which I read when I was thirteen, or the revolutions and leftist-dictators of the twentieth century; and their fictional analysis by George Orwell in his novels.
Having observed human life for several decades, I think the adage that power corrupts is generally true; although I would expand 'power' to include the desire for power - and much the same for fame and status. Having worked in medicine, science and academia generally; I have seen this corruption happen to many people known to me personally, and sometimes very rapidly.
[I have also been tempted into this type of corruption myself a few times, although I have never personally wanted to wield power, and never have done so. But I did desire (and at times achieved) what might be termed influence; and this led to immediate temptations to increase this influence, even at the cost of higher ideals. Fortunately for me; such notions were always, and quickly, sabotaged - willy-nilly - by intrinsic contrariness.]
When I was a teenager, there were many media productions on the theme of power corrupting. For instance, the sixties counter-culture idea of 'selling-out' was a version of this insight - and all the sixties radicals have indeed sold-out: most swiftly becoming managerial-bureaucrats. The leftist trope of 'betrayal' of strikes and other radical movements by their leadership was likewise common currency. I can remember several TV series and plays on this topic.
Yet the understanding that power progressively encourages immorality was actually a relatively modern, post-Victorian, idea - that seems almost to have died-away over past decades.
Despite innumerable confirmations of the theory; people nowadays do not seem to expect power to corrupt as they used-to expect it. Indeed, instead of expecting power to corrupt, expression of the idea is usually treated as an unjust accusation that requires a high (in practice impossibly high) standard of proof.
Why should this be? Why should modern people fail to observe that power corrupts, when it seems so obviously true?
I think there are several linked reasons. One is that power and influence are vastly more concentrated in the world today that ever before in human history - and secondly, that concentrated power is in service to evil.
This leads to general fear - and, this time, fear without the compensating courage of religion.
Fear is one reason why the corrupting effect of power was not visible to the ancient world. Even if one thought it, it was grossly risky to publicly state a theory that the Emperor/ King/ Lord/ Steward was corrupt and getting worse; when he held power of life or death!
Thus, the true-insight that power corrupts was restricted to a time and place in history when people felt safe enough from those with power to be able to articulate the fact.
And we - here, now - are no longer in that time or place.
But even if we cannot publicly and in practice act on the assumption that power corrupts; we ought, nonetheless, to know this in our hearts - and proceed accordingly.