The null hypothesis: "My brain is no better than a coin flip" (50% hit rate).
The z-score and p-value tell you how unlikely your observed hit rate is, assuming the null is true.

p < 0.05: Less than 5% chance you got these results by luck. The brain has edge.
p < 0.01: Less than 1% chance. Very strong evidence of edge.
p > 0.10: Could easily be random. Don't trust the apparent edge yet.

Sample size matters massively: 70% over 10 trades = nothing. 60% over 200 trades = very real. Most traders fool themselves with small samples. The "sample-size needed" stat tells you how many trades you'd need at your current win rate to prove edge.