When the demand for an asset increases while the supply remains constant, a shortage occurs. This shortage happens because more market participants want to buy the asset than there are units available. As a result, the price of the asset tends to rise. This price increase is a natural response to the higher demand, as sellers can charge more due to the limited availability of the product.

Key Points:
1. Increased Demand: More participants want to build position in the asset.
2. Constant Supply: The number of available units does not change.
3. Shortage: The demand exceeds the supply, leading to a scarcity of the asset.
4. Price Increase: Due to the shortage, sellers raise the price, as participants are willing to pay more to obtain the asset.