It's raining hard today, but I have to go out anyway.
Tips
usage
Two senses split by tone of context: 'cannot be said' (taboo, secret) versus 'cannot help but' (forced to act). Tone of voice and surrounding context disambiguate.
register
Slightly literary/colloquial. The 'must do' sense often appears in older novels like 《红楼梦》 (Dream of the Red Chamber).
