It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
Arthur Conan Doyle
To develop a hypothesis is to develop a theory as to the sequence of events that led to the reason or reasons why a problem appeared. Of the tools available to the team, the causal chain is, for me, the most effective. It is one thing to create a long list of potential causes, like you would with a cause-and-effect diagram, but it is quite another to create the actual chain of events that produced the effect.
Causal chains are stepwise evolutions of problem causes. Again, the thought process behind theory development ...