A strategy can appear robust simply because its worst periods were allowed to disappear from the dataset.

Imagine testing a crypto model using only tokens that are actively traded today.

What is missing?

Projects that collapsed.

Markets that lost liquidity.

Tokens that were delisted.

Assets that became economically irrelevant.

Removing those failures from historical research quietly gives the strategy knowledge it could never have possessed in real time.

This is universe-selection bias.

A realistic backtest should reconstruct the investable universe as it actually existed at each historical date—not build yesterday’s portfolio using today’s survivors.

For eligible new users, CODE2026 can reduce qualifying Binance Spot trading fees by 20%, lowering one predictable layer of execution costs.

But accurate costs cannot repair inaccurate history.

The assets that disappeared may contain more information about risk than the assets that survived.

Never ask only how a strategy performed on today’s market.

Ask whether it would have survived the market that actually existed.