Expresses realization or 'no wonder' in response to a previously known fact or situation; means 'indeed' or 'that explains it'.
彼は昨夜ほとんど寝ていなかった。どうりで今日は眠そうだ。
He hardly slept last night. No wonder he looks sleepy today.
電車が遅れていると聞いた。どうりで連絡がないはずだ。
I heard the train is delayed. No wonder there has been no contact.
テストが難しかったらしい。どうりで点数が低い。
The test seems to have been hard. No wonder the scores are low.