Let's give an example of you bought 100 BTC at 9000$ Price and the price went 9010$ in seconds then you sold, so your profit will be 1000$, may 500$ fees, but the another 500$ you made it profit in seconds!
Let's discuss at the point!
One who has the money to invest in Bitcoin $900 000 will not get rich by profiting only $500.
I mean getting loans from people, without interest(sure), then i can make 1 bitcoin in few minutes, then return the money to people, and my deal is success without risk ( as i will hold no more seconds. )