What are your KSP habits? I notice that I have a habit of packing WAY more DV than I needed for the mission at hand. Take for instance my Mun orbiter. I completed the contract, and my transfer stage was half-full, so I did what was obviously the right thing to do at that point...accepted a specific Minmus orbit contract and planned what might have been the least efficient burn I could've planned. I got there...and I had only used half of my probes on-board fuel supply. Oh boy.