In nearly all of my engagements over the last 30 years I and my teams assessed what the problem and solution was very early in the project. We spent the rest of the time and deliverables in the statement of work for the project fleshing out the initial findings. Doing a lot of work without the guidance of up front diagnostics can be very wasteful of time and money.
Example: a medical imaging firm thought the root cause issue was the productivity of its scientists in its R&D shop. They hired a very well know firm for $3 million in fees. The root cause was really a set of convoluted executive processes (strategic planning, budgeting and resource allocation processes overlaid on a convoluted organizational structure) that did not give R&D year to year stability of direction or funding. Our diagnostics pointed to these root causes in five weeks at a fraction of the cost.
A year and a half and $3 million dollars were wasted.