I.
Eureka! is a transliteration from the ancient Greek word εὕρηκα, meaning I've found it! or I've got it! It is related to the term heuristic (i.e. a practical technique for problem-solving or self-discovery).
It is said to have been cried by Archimedes in his bathtub, when he finally realised how to measure with precision the volume of irregular objects and thus determine the purity of gold. Either that, or when he finally got hold of the soap; not all scholars are agreed on what actually happened.
I suppose if he'd been French, he'd have exclaimed Voila! If he'd been English, on the other hand, he might simply have shouted Aha! or Bingo!
The point being that people everywhere and throughout human history have experienced those moments of sudden illumination when all becomes clear at last; what some modern people like to describe as lightbulb moments.
II.
Interesting as all this is, however, what really concerns me here is the possibility of an anti-eureka moment; that is to say, can one feel as if a light has suddenly been extinguished, leaving one bereft of bright ideas and plunged into the darkness of an intellectual and emotional void?
I think so: and probably the Greeks had a word for it; for that fatal moment when one knows that one has lost it ... [1]
F. Scott Fitzgerald suggested that this resulted from an internal blow; one that "you don't feel until it is too late [...], until you realise with finality that in some regard you will never be as good a man again" [2].
That's kind of how I feel at the moment and, trust me, it doesn't make you want to run naked through the streets shouting excitedly. Having said that, there are times when losing the self matters more than finding oneself and, as Fitzgerald also pointed out: life is a process of breaking down ...
Notes
[1] Unfortunately, I don't know (or can't remember) what that word is. In Latin, the term desiderium describes (amongst other things) this feeling of loss (and the sense of shock and grief that one feels as a result of this loss). As for what it is, well, that's debatable; as is the question of whether we can ever really possess it.
[2] F. Scott Fitzgerald, 'The Crack-Up', in The Crack-Up, ed. Edmund Wilson, (New Directions, 1945). The essay was first published in Esquire magazine in 1936 and was made available to read online in 2017: click here.