Simply put, that we don't value what is cheap or free, look, for example, at the environment, the state of our lakes, rivers, the ocean, the air...
Anything that is free is paradoxically worthless - no matter how necessary it is to our survival. Put a price on it, however, and it suddenly acquires a rarity and value worth preserving.
Some examples - Ayahuasca ceremonies, during which the participants retch and shit and discharge their bodily functions all over the mud hut, this, in addition to the tourism fee, is the price, the experience is valued that much more highly than similar or even greater experiences on Mushrooms and LSD are devalued due the fact that they seldom "cost" us as dearly. LSD, DMT, Mushrooms, available at a fraction of the price - are devalued - despite their comparatively mild side effects - and most people that I know claim no sorts of transformative experiences, the "experience" was cheapened by the fact that it was both: A - acquired cheaply & taken out of context B - lacked ceremony, preparation and focus, and C - The mild side effects.
We value what costs us greatly - and the retching, the sickness, this is the part where we're in a sense "Paying" for it, we are more invested in the experience, cognitive bias kicks in and tells us that it was - of necessity - more profound than any other experience we might have had.
It is woven into our language, into our culture, that we pay the price of our career with our family, with our personal relations, that success always comes at a price...
Hence the Faustian bargain and the many legends of people who acquired extraordinary skill or wealth through dealings with the devil.
But note that it wasn't always this way. This is very much The Churches interpretation of the situation.
While wizards formerly were wont to summon the devil to do their bidding, no exchange of souls was necessary. As Cavendish notes,
"The grimoires pay little attention to the Pact with the Devil. Their rituals are intended to subject evil spirits to the magician's control, and when in need of supernatural assistance they seek it from God. From their point of view, to barter away one's soul in a pact is the desperate resort of the second-rate sorcerer."
A curious idea.
**Note - 2 ideas here, related but not entirely. May need to revisit this and rethink it.