So that’s the reason

so Adverb

— How much; very much. The box was so wide that the person was not able to take it through the door.

so Preposition

— With purpose. Saying the reason why someone does something. The person locks the door so no one is able to come in and take things. We help them so that they can get better.

the Determiner

— Used, instead of a, to reference something specific, already known to exist. Compare "I read a book." and "I read the book." — Used with a stress, to show that the word following is special. Are you the John Smith that I went to school with? — Used with an adjective that acts like a noun to mean all of the people concerned The poor are always with us. — Used with superlatives forms of adjectives and adverbs. You are the best.

reason Noun

— A reason to do something is why you do it, or the cause of something. The low price was the main reason for buying it. I asked them about the reason why we should go. The police are looking for the reason for the accident. — Reason is the ability to think clearly. It's important to use reason to decide, not emotion.

reason Verb

— If you reason, you think carefully about something. — (uncommon) If you reason someone, you persuade using reasoning. I reasoned my friend into my religion.