Shi+Xin+Feng wrote:
You could if you had been eating butter all your life. 
Try drinking a different kind of milk than what you are used to. Can you tell the difference between Whole and skim?
If you don't know any better then 'real' is limited to your knowledge and expierences, but it's still real. It's part of how you're raised. If you are told to believe from your birth that cola is actually milk, but no one would ever tell you the lie then it'd still be 'real' milk for you. Everyone else calls it cola.
It's like locking a pet inside a small cage from the first day its born, for its entire life. The pet doesn't know any better and accepts its life and learns to live with it. We find this sad for a pet (I would never do such a thing), but the pet has no choice than to live with it. And if you gave it toys and pet-candy, cheer it up every once and a while then the pet would even be happy. Is such a life for a pet 'real'?
Nope. It's cruel, no pet is supposed to live like that. But that's our perception of what's real, because we know better. We find that all living beings deserve freedom and happiness, which is still just an opinion based on our emotions. For the caged pet it's reality and it could even live a happy life.
(not saying a pet could live locked up all day long. Just overexxegerating the point of taking away all freedom from a living being)
What is real?
Morpheus suggests that 'real' isn't just what you see, smell and can touch. I think what he tries to say is that 'real' is knowing the truth, knowing about your existence, that you were trapped inside virtual reality. But such definition of 'real' is merely an opinion. Because if you don't know any better; would you not live in a real world? 'Real' for me is what I accept it to be until I know it isn't.