I also just thought of this. On the sim, every plane is built perfectly and trimmed perfectly. Every surface is straight, airfoils are accurate, thrustlines are set right, and planes are balanced right. That's rarely true in the real world, at least not until you put the time in to fine tune your plane. So a real plane will be a bit less predictable than the one on the sim. Many beginners won't even notice the difference, but as you progress it can get frustrating when the real plane doesn't make that perfect loop or roll like the one on the sim does without the pilot compensating for that particular plane's quirks.