Hegel's famous quote from the Elements of the Philosophy of Right, "was vernünftig ist das ist wirklich und was wirklich ist das ist vernünftig", typically translated as "the rational is real and the real is rational" ought to be considered one of the most misunderstood phrases among his generally misunderstood work.
For example, the Wikipedia page on Hegel says the following:
"Hegelianism is the philosophy of G. W. F. Hegel which can be summed up by the dictum that "the rational alone is real", which means that all reality is capable of being expressed in rational categories. His goal was to reduce reality to a more synthetic unity within the system of absolute idealism."
What, however, if this is mistaken? On the one hand, for Hegel, following from the Science of Logic, his attempt to begin without presuppositions, to think Being without any presuppositions, from an immediate, unmediated, sheer Being that itself turns out to immediately vanish into Nothing, leads him to the conclusion that the categories of Thought are also the categories of Being, not because we dogmatically assert, that is, assume, this is so, but through a lengthy logical working out. That is, if Thought can think Being without imposing its own presuppositions on it, then, contra the contemporary Pragmatist-influenced reading of Hegel's logic as non-ontological, Hegel's logic is an onto-logic. Following both Slavoj Zizek (Absolute Zero) and Stephen Houlgate (The Opening of Hegel's Logic), both of whom approach Hegel's thought in otherwise quite different ways, I would argue that Hegel proposes a non-dogmatic beginning to philosophy, unlike the modern metaphysics of Leibnitz, Spinoza, and Hegel's own contemporaries, that nonetheless takes seriously the critique of metaphysics pace Kant. To put the matter bluntly, Hegel is making claims about Being in a manner that does not correspond with deflationary notions of truth as argued by Robert Pippin in "Back to Hegel?" in the journal Mediations.
Hegel takes Kant's critique of prior metaphysics seriously insofar as he accepts that metaphysics made assertions about Being that presupposed what had to be proved, but at the same time Kant still presupposes certain things about Being, that is, what could and could not be said about Being, but further Kant simply takes the categories of thought without justification from traditional metaphysics, hence his putting forward of the twelve categories. The result in Hegel's work is the Science of Logic and the attempt to engage the questions metaphysics proposed while keeping Kant's own critique of pure reason in mind.
The end result, and one I would suggest is maintained by Marx, is that the categories of Thought are the categories of Being because the categories of Being can be thought adequately without importation of unjustified concepts by working through Being itself. The dilemmas of philosophical realism, which take for granted and defend the dualistic separation of Thought and Being whether in a (neo-)Kantian mode or an empirical-positivist mode (Trent Schroyer's book The Critique of Domination lays out the distinction between the two reasonably clearly), are fundamentally non-problems from the Hegelian and Marxian perspective. In the case of the latter, this is of course frequently not grasped and so you see nonsense like the split between Dialectical Materialism and Historical Materialism or Subjective Dialectic versus Objective Dialectic and various other dualisms which uncritically reproduce the aporias of dogmatic thought.
Simultaneously, the categories of thought are also not simply imported by Hegel wholesale from prior philosophy, but themselves come into being and disappear and then reappear in different ways. Not all social formations of humanity have access to the same categories of thought and they don't even necessarily think those categories in the same way. This does not mean that all categories of thought are social constructions as if they had no objectivity of their own, since if they are also categories of being they cannot be simply subjective. Nor do "older" categories necessarily have the same character as if they were immutable. This is fairly clear in Hegel's Phenomenology of Spirit, which takes us through many shapes of consciousness, in which many categories appear repeatedly in different shapes of consciousness with differing degrees of determination and concretion.
However, there is a more important sense in which the reading of the original quote from Hegel is horribly mistaken, and that has to do with what Hegel means by "real" or "actual". Most commentators confuse the real with what exists. Of course if this was the case, then Hegel's point would be conservative at best, and really simply a wholesale justification of "things as they are".
Something is real in Hegel in a speculative sense, that is, not because it is materially there or because it is coherent, but because it has possibility. The real and what exists for Hegel are by no means the same thing at all.
Here I just want to end with a practical example of the speculative dimension of Hegel's statement.
Two people are in a long-term intimate relationship and they are nominally committed to spending the rest of their lives together. However, one of them then finds out that the other person has been having sex with their best friend for years. As it turns out, though the relationship existed, it was not real. Of course, the relationship is also then not rational exactly because an intimate relationship between two people involves honesty, trust, and so on between the two people and instead the foundation of the relationship was dishonesty and distrust; essentially a lie. Thus the relationship, which fully existed, turned out not to be real or rational.
We might then say that Hegel's statement is, at its heart, how we ought to read Marx's oft-quoted, always misunderstood:
"Communism is for us not a state of affairs which is to be established, an ideal to which reality [will] have to adjust itself. We call communism the real movement which abolishes the present state of things. The conditions of this movement result from the premises now in existence."
Communism is the real that is rational within capital. Marx does not praise capital in The Communist Manifesto because it is itself great or rational, but because it's potential is communism, which is the rational outcome and inner dynamic of capital (all inner dynamics, if I may use that phrase, for Hegel are those of negation and so a rational outcome is also a self-negation), and therefore the real movement.