Imagine you have been offered a job, and you will be paid in shares. An option is typically more complex than simply receiving the shares (it's an option to receive them), but for the sake of simplicity lets say you have been offered the shares straight up. One hundred of them per month. Lets say the company is called "apple". They are a successful business or at least have many customers.
This might seem like an attractive offer to you right now, because you have some preconceived notion of what a share is and what it is worth. In particular, you have the idea that there are a number of shares outstanding, and this number is public. Everybody knows the number, and somebody or something is entrusted to ensure that no more shares than that number exist. There is thus a thing called a market capitalization, namely that number of shares multiplied by the price one can fetch for a single share in the marketplace.
However, this offer we now consider is different! The shares offered are fiat shares. They are not guaranteed to have a certain number outstanding, nor are you privy to any information about how many are to be released over time. Economists might estimate the amount of shares which have been issued in a given year, but there are no guarantees - nor are each of your shares meaningfully marked or traceable to a certain issuance date. In fact it isn't even clear which people are capable of issuing the shares, as issuance is not publicly verifiable.
Think about it for a minute. How does this change your consideration of the job offer? Are you going to accept fiat shares to take the position? Would you ask for something more sane and less prone to fraud?
To continue in this vein, would you consider buying shares of a company which were issued in this manner? Market capitalization of such fiat shares can only be estimated, now suppose that even the company itself refuses to make such an estimate. Would you recommend others to purchase such shares? Under what circumstances would you trade a bitcoin for 400 such fiat shares?