Present is what matters. The old baggage of past we carry is a burden and it stinks and pollutes our present.
Flowers evolve into tasty fruits. People who have done bad to us in the past might have changed now.
Avoid typecasting. People change with time.
The habit of keeping old grudges in mind affects our mental and physical health. We also knowingly or unknowingly pass it to our children and next generation in the family.
When we constantly discuss our bad past and bitterness, children get influenced by them and ignore the present. Such children keep grudges in mind and get alienated.