You shall make a fence to your roof ... so that the falling person should not fall therefrom (Deuteronomy 22:8).
Rashi notes the unusual term the falling person should not fall and explains that even though the person who may be injured may be "a falling person," i.e. someone who merited punishment for wrongs he or she had committed, nevertheless, you should not be the vehicle for punishment.
Some people act in a hostile manner toward a certain person, even going so far as to condemn him and cause him harm. They may justify their behavior by saying, "Why, that no good ... do you know what he did? He did this and that, and so he deserves to be tarred and feathered."
The Talmud states that God uses good people to deliver rewards, but when punishment is warranted, He chooses people who themselves deserve punishment. Hence, it is not good to be a punitive instrument. The Torah cautions us not to intervene in Divine judgment. God's system is adequate. We should take reasonable actions to protect our interests so that they are not harmed by others, but we should not take upon ourselves to mete out punishment.
The principle of fencing in a roof applies to every situation where someone else might come to harm as a result of something we did or did not do. Being a responsible person requires using reason. As the Talmud says, "A wise person is one who can foresee the future" (Tamid 32a). We don't necessarily need prophetic foresight, just the ability to calculate what might result from our actions.