JRL,
Paper trading is same as when one trades other people's money like those money managers and hedge fund managers. If you are trading with your own money in realtime, no one knows who you are, only market knows and it will teach you, hopefully, you won't pay big $$ to learn.
Trading is nothing but, other people's emotion we are trying to figure out. If we make a lazy trade, other traders who have better emotional control at that time, will make us pay. Look at the SPY chart for the past two months, full of emotions, confusion, pain, angst, profit (still anger, did not make more with big size, etc.). In real trading, even one makes $$, mind acts weird, complaining, why didn't I put more size, why didn't I stay longer, etc.
Hope, this helps. Good luck.