The most expensive mistake on a building site may have cost almost nothing to make. It might be a decision that took five minutes, a detail nobody drew properly, a material selected because it was cheaper, or a problem everyone assumed the contractor would “figure out later.” The irony of construction is that the cheapest decisions are often made at the beginning, while the consequences are paid for much later. By then, changing the decision can mean wasted materials, additional labour, delays, repairs, or compromises that stay with the building for decades.

Buildings are a chain of interconnected decisions. Orientation affects daylight and heat gain. Window design affects comfort and energy use. Structural planning affects construction efficiency. Material dimensions affect waste. Waterproofing affects maintenance. Even the size of a room can influence how efficiently materials are installed. The earlier these decisions are resolved, the cheaper they are to change. Once concrete has been poured, walls constructed and finishes installed, correcting the same mistake becomes considerably more painful. Good design is therefore not simply about producing beautiful drawings. It is about solving expensive problems while they are still cheap problems.

Architecture has plenty of reminders of what happens when design meets physical reality without enough consideration. London's 20 Fenchurch Street, known as the Walkie-Talkie, became infamous when its curved reflective façade concentrated sunlight onto the street below, damaging a parked car and creating dangerously high temperatures. At Walt Disney Concert Hall in Los Angeles, reflections from the stainless-steel exterior created excessive glare and heat, requiring parts of the façade to be treated. These are extreme examples, but most failures are much less dramatic: the roof that keeps leaking, the bedroom that overheats every afternoon, the imported stone that cannot be replaced locally, or the beautiful detail that becomes painfully expensive to build.