The key difference between manual work and knowledge work is that the skills required for manual work change very slowly, whereas with knowledge work, knowledge work makes itself rapidly obsolete.
What this means is that continuous reinvestment in learning and relearning is not simply a fundamental requirement of the knowledge worker, it is an obligation.
What self-reinvestment are you undertaking to avoid your obsolescence?
Adapted from Adam Grant, Think Again, Peter Drucker, Drucker on Asia.