Every instrument pilot should understand the process of filing, getting a clearance, and then flying an IFR flight plan. But why does it occasionally seem that ATC makes things complicated? Say you've filed a straightforward Point A to B then C. But then you're cleared from Point A to B then to X, Y, Z, and only finally to Point C. Why are these extra fixes in the flight plan? Where did they come from? Why this today instead of an intermediate RNAV fix that you usually get?