The DD diagram was developed in 2005 at the UK Design Council (ref)

The process of divergence and convergence are associated with key moments in the design process. Discover and develop phases correspond to divergent processes while define and distribute phases are convergent (…) The path is no longer linear, simply because successive iterations are needed to frame the problem and the solution. (Van der Linden, et al., 2016)

The diagram indicates that the process between divergent and convergent thinking happens twice -once to confirm the problem definition and once to create the solution.

• In the Discover quarter designers try to look at the world in a fresh way, notice new things and gather insights
• In the Define quarter designers try to make sense of all the possibilities identified in the previous phase (prioritize)
• In the Develop quarter solutions and concepts are created, prototyped, tested and iterated (trial and error phase)
• In the Deliver quarter signals the phase where the resulting product is finalized, produced and launched.

References

Van der Linden, J.C.D.S., Lacerda, A.P., Aguiar, J.P.O., 2011. The evolution of design methods. Paper presented at the 9th International Conference of the European Academy of Design, Porto

Images available here and here