Most stats of 6 or more are workable. Below that, and....eh. Reroll.
Low STR? Childhood illness or accident made them frail.
Low DEX? As above, or maybe (for example) a hobbled foot which makes one klutzy. Maybe slight spasms which prevent graceful movement.
Low CON? As above, and more prone to illnesses.
Low INT? Slower to figure things out.
Low WIS? More prone to acting on impulse, more easily controlled by enemy spellcasters.
Low CHA? Suffers from foot-in-mouth syndrome, or generally unlikeable.