“三思而后行”，出自《论语》，意思是“多次思考再行动（think twice before you do）”，形容做事谨慎，小心稳妥。与英文谚语“look before you leap”意思相近，表示“carefully consider the possible consequences before taking action”。
If you deceive your boss now, what do you think will happen if he finds out about it? I mean, look before you leap!
I'm not saying you shouldn't sign the lease for that apartment. I'm just saying you should look before you leap.