It is either Prudent or Painstaking.
careless
The opposite of cautious is: Careless or Hasty
careful
careful; responsible
The opposite word of responsible is irresponsible.
parched
Inaccurate, careless, wrong, faulty.
The opposite of clever would be 'stupid'
Many words could mean the opposite of prudent. Some would befoolish, dumb, stupid, unwise, improper, careless, incautious, rash, inconsiderate, and insensible.
Indifference is the opposite word of concern.
Started
careless = fahrlässig (legal) careless = unachtsam careless = leichtfertig careless = unbedacht careless = unbesonnen careless = leichtsinnig careless = nachlässig