There are people who enjoy making life miserable for others.  They are not happy unless they have made someone else unhappy.  It gives them a sense of achievement to sit by and watch as others reap the consequences of what they arranged to happen.  If these people are coworkers it makes the workplace almost unbearable.  This is true too if it is a family member who is jealous or someone who wants to break up a friendship.

The motives of these people will be exposed in due time by God Himself.  Any vengeance belongs to God.  He has made that very clear that pay back is His. 

When people, for whatever reason, make life difficult He has given specific instructions to return kindness to them.  It is not necessary to become best friends or approve of their actions but only to return kindness.  The greatest act of kindness toward one another is prayer.  God will take care of the rest.

Matthew 5:44-45

But I say: Love your enemies! Pray for those who persecute you!  In that way you will be acting as true sons of your Father in heaven. For He gives His sunlight to both the evil and the good, and sends rain on the just and on the unjust too.