All of us have loved ones who have passed away. They could be a mother, father, sibling, child, uncle and aunt, or a dear friend. You have memories of them and how good they were towards others and towards you. You were impacted by their departure.
But as you got busy with the hustle and bustle of your life, you often forgot to pray for their forgiveness or to give Sadaqah on their behalf.
When that person passed away, they were cut-off from you and everyone they loved. Their opportunities in getting good deeds by their own efforts had ceased to exist. Their test had finished with the soul exiting their body.
The best way to help them is by giving Sadaqah on their behalf.