You do something by accident when you do it unexpectedly.
I found the answer to the question by accident. 我偶然发现了那道问题的答案。
We met again, by accident, at the gym. 我们在体育馆偶然又碰到了。
We met by accident at the railway station. 我们在火车站偶然相遇。
I forgot the cards by accident.我意外的忘了那些卡片。
Sometimes we succeed by accident.有时我们会意外取得成功。
They met him by accident .他们偶然遇见了他。
I meet him by accident.我偶然的遇到他。