"Do'Ha' noybe' wanI'mey'e' bopbogh ghe'naQvam."
Translation:Sadly, the events that this opera is about are not well-known.
The subject in those two sentences represent different concepts in English and so are treated differently. In one case you have a universal, general truth while in the other you have a specific case.
"Animals that eat meat are carnivores" is a case of when you talk about all animals all the time. It is a universal constant. Then you don't need 'the'.
However, "Events that this opera is about are not well-known" is talking about specific events therefore it must use 'the' so it must be "The events that this opera is about..." If you were talking about all events at all times then you would not need 'the'. For example, if you said "Events can also be called happenings." In this latter sentence, you are talking about all events at all times; events here is a universal constant.
Here is an example using happiness:
"HAPPINESS has traditionally been considered an elusive and evanescent thing." This sentence talks about all happiness at all times as a universal idea.
"The happiness I felt that day is something I cannot fully describe." Here you must use 'the' because it refers to a specific limited happiness. It is only my happiness at a specific time not everybody and everything's happiness at all times in all places.
I am sure grammarians have a more official way to explain this. I'll try to find something.
Ah, here is an explanation: