This is the 34th most frequent Bulgarian word.
защото
"Because."
In this sentence, 'защото' introduces a causal clause explaining the reason for not going to the party.
Не отидох на партито, защото бях зает.
I didn't go to the party because I was busy.
In this case, 'защото' provides the explanation or justification for the lack of understanding.
Не разбрах защо ти е толкова важно, защото не ми обясни.
I didn't understand why it's so important to you, because you didn't explain to me.
Here, 'защото' connects the action of studying hard to its underlying purpose or reason.