While society generally espouses the value of logic and certainty, we grow because we doubt. Humans have not spent millennia traversing oceans and experimenting with explosives because of confidence in their beliefs. Culture and science are rooted in unknowns, and when we accept doubt we are more creative and generous, more human. Self-doubt is the indubitable baddie of many aphorisms, but what would life without doubt look like? TL Uglow looks at how writers across the ages have tackled the indecision and uncertainty in the engine room of humankind.