In multicellular organisms it is essential that every cell behaves and does the job it was produced to perform. The survival of a multicellular organism depends on this - every cell in your body is tightly controlled in terms of how big it can grow (fairly big), when it can reproduce (almost never) and what sort of metabolic processes it may carry out. And, like a dystopian sci-fi future, any cell that steps out of line is put to death. Not by surrounding cells, but by its own internal processes.
Each cell in the human body is programmed to die. Death is their default state. It is only by behaving, by obeying outside orders and carrying out the processes it’s meant to, that the cell is able to inhibit its own destruction. This is a good thing for the body as a whole, because cells that do manage to escape the tight death-regulation control are cancerous cells, and cause havoc within the body.