Miànduì wēixiǎn, tā bùjiǎ-sīsuǒ de chōng le shàngqù.
Facing danger, he charged forward without a moment's thought.
Tips
mistakes
The 假 here is NOT 'fake' (jiǎ) but the literary meaning 'to borrow; to resort to' - same as in 假借. So 不假思索 literally means 'without borrowing thought,' i.e. not needing to think at all. Many native speakers don't realize this classical usage.
