fall down

verb3

1. •
   To fall to the ground. To collapse.

   • Ring a-ring o' roses, / A pocketful of posies. / A-tishoo! A-tishoo! / We all fall down. — traditional nursery rhyme (British version)
   • The beams supporting the roof had rotted, causing the entire house to fall down.
2. •
   (figurative) To fail; to make a mistake.

   • That is where your reasoning falls down.
3. •
   To sail or drift toward the mouth of a river or other outlet.