1 to guess what sb will do before he/she does it 猜测；预言: It was impossible to second-guess the decision of the jury. 陪审团的决定不可能预测。

2 to criticize sb after a decision has been made; to criticize sth after it has happened 事后批评；耍事后聪明: There's no point in second-guessing the issue now. 现在事后就这个问题说长道短已毫无意义。