[jerzyt]

Fundamentally, the issue is that in real time you may not be able to make the trade that your algorithm chose. You could get close if you had the actual book prices at any given time, but even then, you might lose to someone who is 1 millisecond faster. So no, backtesting can simulate reality. Interactive Brokers offers a simulated account where you can practice "live" trading, although it's still not the same, since there's no money involved. But if I see a paper tested on an IB simulated account I'll be very interested, and it'll be too late already.

[p1esk]

Good point, but I was mainly thinking about making a single good decision to multiply your investment, not HFT. Like identifying that it was a good idea to invest in Tesla stock 7 years ago.