the.com/backtesting
asking history a leading question until it agrees with your trading strategy.
means simulating a strategy against past market data to see whether it would have made money before you risk it on the future.
from grew out of 1980s quant finance, when cheap computing let traders replay decades of price data instead of just guessing and hoping.
overfitting risktune enough, and any curve fits perfectly
survivorship biasdead stocks rarely make it into the data
lookahead biasaccidentally letting tomorrow's data leak backward
past performancestill legally required to disclaim itself