[slumberdisrupt]

The momentous and scandalous discovery of evolution can only be matched in the field of psychology by the discovery of the unconscious. All of the other responses here do not come close in importance to those massive upheavals you listed.

[Kbelicius]

What do you mean when you say "discovery of the unconscious"? Depending how you define it such an idea was explored since antiquity.

[slumberdisrupt]

That's a fair point, but we should also note that the mighty thinker Aristotle speculated seminal theories of relativity, continental drift, and evolution. I mean Freud's discovery of the unconscious as OP presumably means the discoveries of Einstein, Wegener, and Darwin respectively. Freud's scientific conception of the unconscious was a breakthrough beyond his progenitors.

I'll only admit I've cheated a little: that Freud's contribution was a scientific one is not an assertion that is "generally regarded as correct." But Freud believed himself to be a scientist and frankly I agree. It's not like Einstein, Wegener, and Darwin are uncontested figures, but certainly Freud is much more so.