You obviously don't know the difference.
For EA there is no big difference trading demo vs. real. On good broker there are very similar conditions.
For manual trading there is a psychological aspect as you cant accept loose of 10000 real dollars compared to demo:)
Agree there is no big difference with EA short term, but there is a difference. For example, on a demo comparison I tried, demo gave me no gaps or slippage and the swap rates lagged behind the real account. I also had no-fills on real (out of price errors) while demo filled orders regardless (causing the most impact). These add up quickly to a huge difference in outcome (note I say outcome not strategy or method). It really comes down to how the broker sets up the demo vs real servers, some will follow real principles, others set them up to just run as efficiently as possible for trading practice (not meant to represent real trading environments). On manual trading the variables become even greater as you are more likely to trade at higher risk, less emotion (in the beginning) and with a 'try and test' attitude on demo than with real.
For every loss there should be at least an equal and opposite profit.