Your cactus/pothos/philodendron/succulent died after you had worked so hard on making sure it had the perfect environment to grow in.
I have done the same. I have even killed plants that people say are “easy” or “indestructible.” If you ask anyone who has collected plants, they will say the same thing—even the most prominent gardeners in the world. But why did my plant die? You could have had everything just right for your said plant; you were watering it the necessary amount, gave it the proper lighting, planted it into the suitable soil, but unfortunately, the plant still passed away. So what happened? There are different reasons plants might die, and I will review them here. Hopefully, this awareness will help to provide your plants with the best chance possible for success!