The Challenge
Almost every new contractor makes the same mistake Sarah made, and it doesn't feel like a mistake while it's happening. Winning nearly every estimate feels like proof you're good at the business. A packed schedule feels like success by definition. Both feelings can be completely true and completely misleading at the same time, because neither one has anything to do with whether the jobs are actually worth doing.
Most contractors don't fail because they can't do the work. They fail because they never learned to price the work like a business owner instead of a tradesperson still thinking in hourly wages.