No matter what sort of change is going on in your industry, if you don’t teach people why to do things differently and what to do differently, they will do the same old stuff.

Effective training doesn’t just happen once. It doesn’t just cover theory. It explains exactly what to do, and it reinforces these new tactics again and again, over many months.

Source: A Fool with a Tool Is Still a Fool

Some great information on running PD, more importantly, planning PD.