защото

In a sentence

• Не отидох на партито, защото бях зает.

  I didn't go to the party because I was busy.

  In this sentence, 'защото' introduces a causal clause explaining the reason for not going to the party.

• Учих много усилено, защото искам да постигна добри резултати.

  I studied very hard because I want to achieve good results.

  Here, 'защото' connects the action of studying hard to its underlying purpose or reason.

• 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.

  In this case, 'защото' provides the explanation or justification for the lack of understanding.