Sounds cliched, but the remaining 10% is real world experience applying and reflecting on a myriad of (sometimes pseudo-) psychology concepts developed over the years in the areas of leadership, self awareness, and workplace behaviour.

Probably more like 50%. I got an MBA and pretty much realized I had very little interest in actually being a manager.

I think there’s a lot of ‘teachings’ in those books, but the applying and reflecting it is the ‘10%’.

I also did an MBA, but my incentive was mainly for the technical skills. Ive been lucky in that I’ve always worked in high performing and highly experienced teams within my industry (th cybers), so the need to ‘manage’ people is somewhat moot, but it did teach me a lot about managing and influencing and coaching other less experienced (or unprofessional) teams and stakeholders.