tā / huí / xiǎng / qǐ / nà / duàn / wǎng / shì / bù / jīn / jiē / huǐ / dāng / nián / de / jué / dìng

他回想起那段往事，不禁嗟悔当年的决定。

Thinking back on those events, he could not help regretting his decision at the time.