un·do·ing 
/ˌʌnˈdu:wɪŋ/ noun
/ˌʌnˈdu:wɪŋ/ noun [singular] 1 : something that causes someone's failure, ruin, etc.
▪ My quick temper was my undoing. 2 : a state of failure, ruin, etc.
▪ His quick temper helped lead to his undoing. ▪ The incident resulted in her undoing.
▪ My quick temper was my undoing.
▪ His quick temper helped lead to his undoing. ▪ The incident resulted in her undoing.
