How to say you must be more careful to avoid making a gross mistake. in Japanese
1)
あなたあなた(anata) (pn,adj-no) youはは(ha) (int) indicating a subject/yes/indeed/well/ha!/what?/huh?/sigh大き大き(ooki) (pref) great/grand/large/greater/upper/senior/a great deal/very muchなな(na) (prt) connects adj to noun/indicates emotion or emphasis/command/prohibition間違い間違い(machigai) (n) mistake/error/blunder/accident/mishap/trouble/improper conduct/indiscretionをを(wo) (prt) indicates direct object of action/indicates subject of causative expression/indicates an area traversed/indicates time over which action takes place/indicates point of departure or separation of action/indicates object of desire, like, hate,しし(shi) (num) 10^24/septillion/quadrillionないない(nai) (aux-adj) not/emphatic suffixようもっとno dictionary result, likely a conjigated verbno dictionary result, likely a conjigated verb気気(ki) (n) spirit/mind/heart/nature/disposition/motivation/intention/mood/feelings/atmosphere/essenceをを(wo) (prt) indicates direct object of action/indicates subject of causative expression/indicates an area traversed/indicates time over which action takes place/indicates point of departure or separation of action/indicates object of desire, like, hate,つけなければならno dictionary result, likely a conjigated verbno dictionary result, likely a conjigated verbないない(nai) (aux-adj) not/emphatic suffix。。(。) Japanese period "."
