Trading outcomes over short stretches are dominated by variance (luck), not skill. A great week doesn't prove your edge; a brutal one doesn't prove you're broken. Confusing the two — changing a good strategy after a bad run, or getting cocky after a lucky one — wrecks otherwise-competent traders.
Why small samples lie
Even a genuine edge with positive expectancy produces losing streaks and winning streaks purely by chance. With a 50% win rate, runs of five straight losses happen regularly — that's normal variance, not a broken system. Over 10 or 20 trades, the noise is far larger than the signal, so the results tell you almost nothing about your actual skill. You need dozens to hundreds of trades before the average starts reflecting your edge rather than your luck.
The two failure modes
Overreacting to a bad run: abandoning or overhauling a sound strategy because of a variance-driven losing streak — then doing the same to the next one, never giving any edge time to show. Overreacting to a good run: concluding you're a genius, sizing up recklessly, and giving it all back. Both come from reading skill into what was mostly noise.
Five wins doesn't make you good; five losses doesn't make you bad. Over small samples you're mostly measuring luck — judge the process, and let the sample grow.
How to think instead
Judge yourself on process over outcome, evaluate your edge only over meaningful samples in your journal, and expect streaks in both directions as normal. Size to survive the streaks. Patience with variance — not reacting to every wiggle in your equity curve — is itself a skill, and a rare one.