there is a large degree of flexibility within the relationship to change and adapt based on external forces (the world) and internal forces (from within the relationship). Tendency towards change and evolution rather than stagnation
This one seems like it too should be obvious.
It's impossible for our logical minds to "see" all that is coming in life. If we aren't flexible-we die.
It's really THAT plain.
In every situation we ever encounter there is the possibility of the unexpected to occur. If we aren't flexible-it will destroy us.
In trying to limit flexibility in our relationships we limit flexibility in ourselves AND in our partners which causes both our demise, their demise, the demise of the relationship (eventually) and ultimately the demise of mankind.
All things change, the world is in a constant state of change, our ability to change is the key to our survival. We MUST evolve to survive because the world around us is changing, every minute.
If we don't-first comes stagnation.
But the end result is extinction.