Level 5 · Advanced
The reason why: 之所以…是因为
Subj. + 之所以 + Result，是因为 + Reason · Traditional: Subj. + 之所以 + Result，是因為 + Reason
之所以…是因为 (zhīsuǒyǐ…shì yīnwèi) flips the usual cause-first order: the result comes first, spotlighted, and then the reason is revealed — 我之所以迟到，是因为路上堵车 "the reason I was late is that traffic was jammed."
Use it when the result is already on the table and you're explaining it. Note that 之所以 attaches after the subject, and the reason clause needs 是因为 (or 是为了 for purposes), not bare 因为.
Examples
我之所以迟到，是因为路上车太多。
我之所以遲到，是因為路上車太多。
wǒ zhī suǒ yǐ chí dào shì yīn wèi lù shang chē tài duō
The reason I was late is that there was too much traffic.
他之所以成功，是因为从来不放弃。
他之所以成功，是因為從來不放棄。
tā zhī suǒ yǐ chéng gōng shì yīn wèi cóng lái bù fàng qì
The reason he succeeds is that he never gives up.
这家店之所以有名，是因为菜特别好吃。
這家店之所以有名，是因為菜特別好吃。
zhè jiā diàn zhī suǒ yǐ yǒu míng shì yīn wèi cài tè bié hǎo chī
This restaurant is famous precisely because the food is amazing.
我之所以告诉你，是因为我相信你。
我之所以告訴你，是因為我相信你。
wǒ zhī suǒ yǐ gào sù nǐ shì yīn wèi wǒ xiāng xìn nǐ
The reason I'm telling you is that I trust you.
Common mistakes
✗ 之所以他成功，是因为他努力。
✓ 他之所以成功，是因为他努力。
之所以 goes after the subject: 他之所以…, not 之所以他….
Related grammar points
Practice this pattern in graded stories like Talking Price (Part 4) inside the Literate Chinese app.
