Definition of 今是昨非 (こんぜさくひ)

expression
complete reversal of values or ways of thinking (over time), What appeared wrong in the past now appears right, realizing and regretting the past errors of one's ways(yojijukugo)
Related Kanji
now
just so, this, right, justice
yesterday, previous
un-, mistake, negative, injustice, non-