Five primary causes: incomplete scope in the original estimate (items not included appear as change orders after work begins); allowances set below market-realistic levels (actual selections exceed placeholder amounts); undocumented verbal scope changes that accumulate without client approval; material cost increases for long-duration projects; and the absence of real-time cost tracking (overruns are not visible until the final invoice). The first three are estimates and change order management failures. The fourth is mitigated by early ordering. The fifth is what job costing specifically addresses — a project with real-time tracking produces early warning when actual costs diverge from budget, while a project without it produces the same information only at final invoice, when intervention is impossible. RainFire Builders applies countermeasures to all five causes.