Volatility measures how much a price moves around its average. A fund with 18% annual volatility will have +25% years and −15% years without anything extraordinary having happened.
It is worth separating from risk. Risk, for someone saving over thirty years, is failing to reach the goal; volatility is merely the admission price charged by the assets that historically make it reachable. A savings account has no volatility and carries enormous risk against that goal: the certainty of losing purchasing power to inflation.
Where volatility becomes real risk is when it forces a sale: because the horizon was shorter than assumed, because there was no emergency fund, or because the size of the fall was unbearable.