kǔ​zhōng

troubles

苦衷 kǔ​zhōng
troubles noun
difficulties, painful feelings, or secret troubles that are hard to speak about or reveal to others

The reason he did this was actually because he had some unspeakable difficulties.

Frequency

Movie subtitles
1.64 per million appears in 1% of films
Written text
1.86 per million

Sources

Definitions
CC-CEDICT