Since you trade about 20 times a day and said your back test gave you 100% a year, your average gain per trade is about 0.02%, which is dangerously close to the slipage and other losses due to execution. However, without going live you'll never know. From my own experience execution problems (delay, slipage,etc.) easily cost me 0.02% per trade. So that's the first thing you want to watch closely once going live.
This is not an expression, I believe it is a quote from Albert Einstein. I believe the exact quote is, "Everyone knows something cannot be done. Then along comes a man who does not know that it cannot be done and does it." One of my favorite quotes.