Jolead19 wrote:I'm looking for a book on investing that specifically is not about shares (I probably have all of them already)
Accepting that the question is rather vague, then studying human behaviour is likely to prove very beneficial.
If you're happy with the "market return", then you can simply invest in the market (ie. a proxy for the market portfolio), do nothing, and await your eventual long term returns. Job done - almost. Almost, as to "do nothing" may be harder than you expect. Understanding human behaviour, and thus your own behaviour and your (emotional) responses to the behaviour of others, will prove useful in staying the course.
But if you want a shot at a different (better) outcome than the market return then you need to do something different to what everyone else is doing. Whatever framework you adopt will, by necessity, have at its core the need to have you behaving differently to other investors in aggregate, in order that you enjoy an outcome different to other investors in aggregate.
So study human behaviour: understand the intrinsic mental heuristics/biases that repeatedly trip people up, then consider ways to turn these into advantages able to deliver better-than-market returns.
Read up on behavioural finance/economics and psychology as it pertains to markets and in general. And practice zen-like suppression of your own ego, which otherwise always trips people up, whether investing or in life in general. As someone maybe once said:
"Before you make any decision, stop...and set aside your ego."