thoughtlessness; indiscretion; lack of judgment
Describes acting without careful thought or good sense; often used for rash or imprudent behavior.
His thoughtless remark made the problem worse.
When I was young, I often acted without thinking.
無分別 stresses a lack of judgment or discretion, whereas 非常識 stresses a lack of common sense specifically about social norms.
無差別 (indiscriminate, treating all the same) and 無分別 (thoughtless, imprudent) look similar with their 無...別 pattern but have unrelated meanings.
Compound of 無 (mu, 'without') and 分別 (funbetsu, 'discernment, judgment'). The word follows a common Sino-Japanese pattern for negation.