A consequence of the Dutch unrealized capital gains taxes is that it will cause a lot of forced selling on January 1st every year. They don't *have* to sell then, but if they don't they're rolling the dice that the price of the assets they own will hold up. In principle market makers, funds, and other financial actors step in to absorb the sudden and concentrated demand for liquidity, but this might so unprecedented that there may be leftover capacity for that trade even after the professionals step in.