[rcxdude]

The best way of thinking about it I have come across is that your plan for doing X in the future is allowed to be "We change the code to extend it to do X in the future". Flexibility doesn't need to mean you build something now to make it so you can add X by only writing new code in a neat little module, it can also be that you can just change how the code works across the system to accomodate X. In fact, if you focus on making the latter kind of changes easier, you'll do better in general, and that generally means keeping things simple.