[Programming] There is no such thing as straight and level. Even if things seem to be going perfectly, you don’t take your eyes off the road. Change is the only constant. Always be prepared to move a little this way, a little that way. Sometimes maybe you have to move in a completely different direction. That’s life as a programmer.
Everything in software changes. The requirements change. The design changes. The business changes. The technology changes. The team changes. The team members change. The problem isn’t change, per se, because change is going to happen; the problem, rather, is the inability to cope with change when it comes.
in Extreme Programming Explained