expression, noun
no wonder; as expected; of course
Expresses that something is only natural or to be expected given the circumstances. Often used in response to new information that confirms a prior assumption.
彼は毎日練習しているから、上手なのはそのはずだ。
He practices every day, so it's no wonder he's good.
あの店はサービスが悪いから、客が来ないのもそのはずだ。
That shop has bad service, so it's only natural that customers don't come.
当然 is a more formal and objective statement of natural consequence, while そのはず is a colloquial phrase that often carries a nuance of 'I knew it' or 'that explains it'.
なるほど expresses understanding or agreement with new information, while そのはず asserts that the information was expected or is only natural.
Combination of その (that) and はず (expectation, should be). The phrase literally means 'that should be the case' and developed into a fixed expression meaning 'no wonder' or 'as expected'.