Define a contingency
What are all the possible ways for the best possible solution to go wrong? Every task can be subject to multiple conditions needing to be favorable. Even if one doesn’t happen to be desirable, a contingency is needed as a buffer.
Most companies call in consultants to solve problems that need subject matter expertise outside of that company’s reach. So the project team would have client’s own employees along with contractor and consultants hired to implement a project to solve a problem or to better an existing solution.