原版书有一个例题大概意思是，有A,B两个portfolio，market value 都是10m，A 是overvalue，B是undervalue。如果投资者需要10m现金的话，需要怎么操作。假设投资者是taxable的。
原版书的回答是100%卖 B, 因为卖A有 capital tax。
我的问题是，为什么不能卖50%A+50%B？ 这样B的capital loss 刚好可以抵消 A的capital gain，而且不用全部卖完undervalue 的B, 剩下50% B还有可能升值。
以下是原版书的解释
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All else equal, portfolio managers for taxable investors should have an incentive to defer capital gains taxes and realize capital losses early (tax-loss harvesting) so that losses can be used to offset current or future capital gains. Despite the slight undervaluation of the position, the portfolio manager might want to liquidate Position B because of its embedded capital loss, which will result in a lower realized net capital gain being distributed to investors. This decision is based on the assumption that there are no other capital losses in the portfolio that can be used to offset other capital gains. Despite the slight overvaluation of Position A, its liquidation would be less desirable for a taxable investor because of the required capital gains tax.
