An ancient Sanskrit saying has it:
तुंडे तुंडे मतीः भिन्ना।
(tunde tunde mateehi bhinna)
Which literally means that every head has a differing mind. Less subtly, everyone has a different opinion.
It may remain unsubstantiated at this hour, but I would argue that this difference and diversity is stemming from the ‘Genetic diversity’ as found prevalent as a principle under Biodiversity as a hole. Biodiversity, in a sense, is a science of studying all the various species and their interdependence that gives the significance to the ecology and bio-ecosystem of the Earth. Taken a few logical steps further on the same line, this would translate into the social phenomenon classified as Cultural diversity, and so forth.
It is the Mind, the psychology, that divides and at the same time units all individual aspects under the single ecology of the cultural fabric.
In other words, things are as they are in the world, good or bad, because of this Diversity principle - what may be considered good for one may not be good for someone else... If one applies this theory to the state of one's living, saying that the solution to your given prevailing unfavourable personal condition lies is a certain product or service, one becomes a party to the economy. For this very principle is also an integral part of world economy. (Look around and you would find examples are aplenty.),
It is that Gap, disparity, demand vs. supply, the fundamental logic behind any economy, that gives goals and 'purposes' to individual lives in the contemporary world.
And, as we just argued, that gap, the economy, stems from Mind, the psychology.
Having said that, one may approach psychology through economy and argue that - economy also contributes into framing of an individual psychology. Which is absolutely true as well - for economy is largely responsible for the socio-political environment one lives in. This environment influences one's thought process all the way from childhood - which the psychoanalysts know as conditioning of the 'mind'.
So, I suppose it is safe to say that both of these are like best buddies, going hand-in-hand, none leading the other, nor one following the another. They are like the two aspects of the duality that is so omnipresent in the world at large.
These two, always co-joined, create what I would want to call a Mind Gap, which is perhaps more significant than all other gaps – generation gap, cultural gap, socio-political gap, et al. And it is this combination of psychology and economy that rather 'rule' and 'runs' the world.
Mind, the Gap.