David Anderson writes about Drucker on Effectiveness, finding a number of interesting quotes, including that in the title of this post.
He goes on to observe that effectiveness is not achieved from principles but from successful execution of practices. If we are to learn from Drucker, it is that we cannot merely talk about agile development in abstract principles - even though this is the simplest way to gain consensus in the community - in order to show effectiveness we must articulate practices which deliver productivity.
Excellent! This is in line with where I have been thinking recently too. Effectiveness isn't a personality trait, it is a skill and habit that can be practiced and learned. But it does have to be practiced and learned for it to become part of your personal toolbox.