#TradersLeague The fundamental principle that makes trading work is the connection between supply and demand. When there are more buyers than sellers, demand increases — and so do the prices. When sellers outnumber buyers, demand shrinks, causing prices to fall.and most people who try it end up losing money. According to both academic and industry research, the success rate in day trading is quite low. Depending on the source, only around 3% to 20% of day traders make money.