What is the word describing in a plot the protagonist realizes his previous actions all wrong

Solution 1:

I do not have the Norton Critical Edition of Burgess’s novel to hand, but I would strongly suspect that the word is anagnorisis (ἀναγνώρισις), a term of art in Aristotle’s analysis of tragedy, meaning recognition or discovery:

A “discovery,” as the term itself implies, is a change from ignorance to knowledge, producing either friendship or hatred in those who are destined for good fortune or ill. A discovery is most effective when it coincides with reversals, such as that involved by the discovery in the Oedipus. There are also other forms of discovery, for what we have described may in a sense occur in relation to inanimate and trivial objects, or one may discover whether some one has done something or not. But the discovery which is most essentially part of the plot and part of the action is of the kind described above, for such a discovery and reversal of fortune will involve either pity or fear, . . . [Poetics 1452a]

Aristotle is being very general here as usual, but Alex’s recognition surely qualifies.

Solution 2:

I'm not clear if the word you describe was in the novel itself or in commentary to the novel, but possibly it could be "epiphany." An epiphany is: a realization on a large scale, a revelation, something life-changing in its effect; something which transforms a person completely, particularly in the sense of shedding new light on old situations. It is a word used often in religious contexts, as in the Bible story about the Magi realizing the Christ Child has been born as represented by the star.

Solution 3:

Being as anagnorisis has been provided already the modern equivalent might be the "reversal" -The reversal should be the consequence of the critical choice and the climax, and it should change the status of the characters, especially your protagonist.

Solution 4:

Another phrase from Christianism is "Damascus experience", referring to the conversion of Saul to Paul, which happened on the road to Damascus.