It's Aliiiive!
Your software is alive!
I'm not kidding.
Software projects take on a life of their own. You never end up quite where you started.
Stuff you thought would be hard ends up being easy.
What seems like a simple change can take down your entire infrastructure.
Strange bugs pop up out of nowhere, years after things have been "working fine".
Don't treat software as a physical object that is built and then done.
Right from the beginning, plan an agile approach to care for and feed your constantly evolving project.