On this LinkedIn discussion there is this interesting question.
And here is the unconventional, Guerilla answer. It does not talk about lack of risk management or planning.
I believe they don't teach you:
1. how to be mentally tough; since being a Project Manager is a stressful job. This is a skill that all PMs, especially Guerilla PMs, must master; or they will soon become unable to enjoy their journey to completing the project.
Moreover, I consider mental toughness a life skill in business world; kinda like speaking English. There is definitely no literature on that topic directed at Project Managers; but there is some literature aimed at business people and managers in general. Most of what I've read is trash, but Developing Mental Toughness is one book that I enjoyed and learnt a lot from. It is still my reference whenever I am feeling stressful or in doubt.
2. about business; I believe it is very important for a Project Manager to be generally knowledgeable about business (e.g. Quick MBA).
First you need to understand how a business is run in order to understand what drives each of your stakeholders; then you need to understand how your project fits in the overall business model of your client.
3. how to be creative, or at least that it is necessary to be creative: in finding resources, in finding solutions to multiple constraints, in motivating your team with no budget.. and many other situations. There was a poster saying "Everything is possible if you have an endless amount of resources at your disposal".. and this is how most of the PM courses are taught. Real life projects are not like that, except perhaps if you work for DoD.