Backtesting or forward testing: which taught you more about your own edge?

A backtest runs a strategy on past prices. A forward test runs it on prices as they arrive, which makes it harder to fool yourself. Members disagree on which teaches more, and many use both. MetaTrader 4 vs MetaTrader 5 vs cTrader vs TradingView compares the platforms many members use for testing and trading, and the choice of platform affects how much detail a test can capture.

A backtest can look excellent and still fail once real spreads, slippage and emotions are involved. The gap between the two is useful information in itself. Members who keep both records often find that the backtest was optimistic in the same places each time, and that the forward test showed where the rules were unclear. A strategy that only works on the historical data is not yet a strategy you can trade.

We would like to hear your experience:

• Which method did you rely on first, and what did it show?
• Where did a backtest and a forward test disagree, and which did you believe?
• How do you account for spreads, slippage and fills in a test?
• What would a test need to show before you trust it with money?

Please share your own approach and reasoning, not calls for others to copy. Posts that promise a direction or sell signals will be removed.