Profitable on paper, broke in reality
Here is the uncomfortable fact that catches out many beginners: a strategy with a genuine, positive edge can still lose all your money. Edge tells you what happens on average over the long run, but variance decides the path you take to get there — and if your position sizes are too large relative to your portfolio, a normal losing streak can wipe you out before the average ever arrives.
What risk of ruin measures
Risk of ruin is the probability that you lose your entire portfolio before your edge can play out. It pulls together the three things that actually decide survival: how big your edge is, how large each position is relative to your capital, and how much variance your strategy carries. Change any one and the number moves — which is exactly why none of them can be judged in isolation.
The levers you control
You rarely control your edge precisely, and variance is largely fixed by the markets you play. The lever you fully control is position size — and it is by far the most powerful. Halving your position size can take a dangerous risk of ruin and make it negligible, at the cost of slower growth. That trade — a little speed for a lot of safety — is the central decision of portfolio management.
Aim for negligible, not just low
The goal is not a low risk of ruin, it is a negligible one — small enough that going broke from variance alone is effectively off the table, leaving only the slow, recoverable kind of drawdown. Use a simulator to find the position size that pushes your risk of ruin toward zero for your edge and portfolio, then size at or below it. Survival first; growth second.