Isn’t it curious—by which we mean ludicrous—that more than half the projects on this planet stagger forth with precisely the same contingency budget, as if fate itself had standardized its malice? Risks differ, contexts vary, suppliers wobble, currencies sulk, and yet the priesthood assures us that one charm repels all demons.

Every tribe has its talisman. In childhood it was mother’s kiss: a sacrament applied to a scraped knee with miraculous results. On the football pitch—soccer, if you must—the anointed object is the damp sponge. A man writhes as though auditioning for the Last Rites; a sponge is dabbed; Lazarus sprints.

Projects have their own sponge. It goes by “contingency” or “tolerance,” depending on which catechism you recite. And—here is the true enchantment—it is always ten percent. Not eight, not fifteen. Ten. The digits march like Roman soldiers: And. It. Is. Always. Ten. Percent.

This, in a sane world, would be the point at which someone asks whether the margin of error might have something to do with reality. With how well we know the domain. With the volatility of prices, the fragility of suppliers, the novelty of the technology, the competence (or absence) of the team, the brutality of the schedule. But no: bring forth the silver bullet that fits every caliber.

Why ten? Nobody knows, and—more damning—nobody seems embarrassed not to know. Perhaps, in some ancestral spreadsheet, ten percent was a defensible hedge for one specific undertaking. Perhaps a standards committee embalmed it, and the embalming fluid spread across the corporate bloodstream. Or perhaps it diffused the way all superstitions do: because it was tidy, repeatable, and made the anxious feel insured against the weather.

Whatever the origin, the effect is the same. A risk unpriced is a risk unmanaged, and a risk priced by numerology is managed by nobody. 

The adult alternative is not mystical: quantify uncertainties, model ranges, revisit as information improves, and fund the consequences. Some projects deserve two percent; others, twenty and a prayer. Only a cult would insist they all merit the same tithe.

But then, magic has its consolations. You don’t have to think; you don’t have to argue; you don’t have to tell the Steering Committee that the gods may be angry and that appeasement will cost more than a round number. You can intone “ten percent” and pass the peace.

As with all talismans, the power is in the believer, not the object. And as with all talismans, reality eventually intrudes.