In a consulting project, a typical consulting firm will start by coming up with a hypothesis about the problem facing the client. It will then gather information from various sources including market research and data provided by the client. The firm will analyse this information using statistics, consulting methodologies, and industry experience. The firm will then provide recommendations to the client supported by its analysis.
A consulting firm's analysis will often be reliable. But it has its limitations, such as the consulting firm may have limited data on which to base its conclusions, or the consulting firm may hide the limitations of its analysis in order to justify the high fees it charges to the client.
However, even if the analysis undertaken and recommendations made are sound, this does not guarantee that they will lead to positive financial results for the client. For example:
A client may fail to implement the advice which it has received.
Market conditions may change which invalidate previous advice. For example, the CEO resigns, a major competitor enters the market, or a new technology is invented.
The economy may enter a recession.
The earth might get hit by an asteroid.
Etc.