A positive edge still goes to zero if every trade risks too much. Size is the variable that kills accounts.
Risk of ruin is the probability that a long run of variance drains the account before your edge can pay off. It is driven mostly by one number: how much you risk per trade. A trader with a real edge risking 5% a trade can still blow up; the same trader at 1% almost never does. Survival is not a bonus — it is the precondition for compounding, because you cannot trade an edge from a dead account.
Win rate barely moves risk of ruin; position size dominates it. Roughly, double your size and you square your odds of a deep hole. The reason is streaks: every system has a losing run worse than any you have seen yet, and size decides whether that run is a drawdown you climb out of or the end of the account. Variance always gets a vote — sizing is how you keep its vote small.
Treat anything above roughly 5% risk of ruin as a sizing problem, not bad luck. Cut risk-per-trade until the estimate falls — smaller size raises survival odds sharply. Set the stop before entry and never widen it, so a full stop is your planned 1R every time. A worst loss well past 1R means the stop moved or the size was wrong, and that is the leak to close first.
Reading about R is the easy part. The journal makes you keep the stats — grade the setup before you know how it ends, and hear the one thing to fix next.
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