To start with the discussion of the above-said topic, I wish to take a real-life example:
Imagine a husband and a wife, living in the same house, are not communicating with each other. Or let’s say there is nothing to communicate between them. They just text each other if anything important needs to be taken care of. Otherwise, both are busy with their own lives and do not disturb/take care much about each other. What happens after days? A frustration rises, irritation multiplies, anger surfaces and finally an explosion occurs. Any relationship strengthens only if there are frequent communications, rare fights and multiple agreements and celebrations exist with each other.
Now, compare the above situation with the software project lifecycle.