A quoted price describes the last small trade or the best current offer. It says nothing about how much could actually be bought or sold near that level.
An order book is a ladder, not a price
Orders rest at many different levels, with quantities attached. The quoted price is only the top of that structure, representing the best available at that instant.
Executing a larger order consumes the quantity at the best level, then the next, and so on. The average achieved is worse than the quoted figure.
Depth measures how much sits at each level. A deep book absorbs size with little movement; a thin one does not.
Slippage is the cost of thin depth
The difference between the expected price and the achieved average is slippage. It grows with order size and shrinks with depth.
For small trades it is negligible, which is why it is easy to overlook until a larger position is being established or exited.
The cost is not a fee and does not appear as one. It is embedded in the execution price.
Depth varies by venue and by time
Liquidity is fragmented across venues, and the same asset can be deep on one and thin on another. A quoted price on a small venue may be unrepresentative.
Depth also varies through the day and collapses during periods of stress, which is precisely when participants most want to transact.
This is why the ability to exit a position cannot be assessed from normal conditions alone.
Thin books distort the quoted price
Where depth is minimal, a relatively small order can move the quoted price significantly. That new price is then displayed as if it were a market-wide valuation.
Assets with low trading activity can therefore show dramatic price movements that reflect the absence of orders rather than any change in assessment.
Valuing a holding by multiplying quantity by the quoted price assumes depth that may not exist.
What to look at instead
Sustained trading volume, the spread between best bid and offer, and the quantity resting within a range of the mid price together describe tradability better than price alone.
Placing limit orders rather than market orders puts a boundary on execution price, at the cost of not being certain of filling.
None of this indicates whether an asset is worth holding. It describes what transacting in it will cost, which is a separate and often ignored question.