Contractors will be extreme sticklers about their requirements on a project. So that if anything starts look off-plan or may impact something like a schedule de

Contractors will be extreme sticklers about their requirements on a project. So that if anything starts look off-plan or may impact something like a schedule delay they will say "nope, that's outside of our scope of work we need an extension/additional funding". Yup, change orders are how deal with these issues when it comes to fixed-costs contacts. For better or worse, its almost impossible for a project to be perfectly specced out ahead of time. And anything that even comes close to looking like it conflicts with the spec becomes a change order.