Holding a grudge is like trying to get revenge on someone else by hurting yourself.
If you're holding a grudge today, find a way to genuinely forgive that person. Just think how many opportunities you are allowing to slip by just because you are unwilling to forgive and forget. Stop hurting yourself with your own foolish pride.
Judge not, and you will not be judged; condemn not, and you will not be condemned; forgive, and you will be forgiven.