许多主动型基金经理人相信，被动投资的崛起终将因市场无效率而为主动选股者带来转机。然而，一项由学者 Hannah Unterberg 发表的新研究指出，资金流向被动基金反而对主动型基金的绩效造成了结构性打击。当资金从主动管理转向被动指数基金时，经理人被迫卖出其重仓股，而被动基金则依指数权重买入，这种「资金流向引起的非对称价格压力」持续打压了主动型经理人的优势持股。

虽然该论文提供了解释主动型基金绩效下滑的数据支持，但金融时报的 Alphaville 专栏对此论点提出了质疑。专栏指出，主动型经理人在面临赎回时，并不一定会成比例地削减其最看好的重仓股，且主动型投资人依然是市场的价格制定者，被动基金则是价格接受者。因此，资金流向造成的价格压力可能不足以完整解释主动型基金所面临的长期困境。

作为替代解释，专栏引用了 Michael Mauboussin 的「扑克牌桌理论」。该理论认为，被动投资的兴起淘汰了市场上平庸或差劲的基金经理人，使得留在市场上的竞争者都是实力最坚强的对手。因此，主动管理变得更加困难，并非因为经理人技能退步，而是因为对手变得更加聪明且竞争更加激烈，市场中缺乏可以轻易赚取超额报酬的「弱者」。

Many active fund managers believe that the rise of passive investing will eventually create market inefficiencies, leading to a comeback for stock pickers. However, a new paper by researcher Hannah Unterberg suggests that capital flows into passive funds actually deal a structural blow to active performance. When money shifts from active to passive vehicles, active managers are forced to sell their preferred overweight positions while passive funds buy according to index weights, creating an asymmetric price pressure that persistently punishes active tilts.

While the paper provides empirical support for the decline in active performance, Financial Times' Alphaville raises doubts about this specific argument. The column notes that active managers suffering outflows do not necessarily pare back their most favoured overweight positions, and that active managers remain the price setters while passive funds act as price takers. Therefore, flow-induced demand might not be the primary driver of active managers' ongoing woes.

As a broader explanation, the column introduces the "Poker Table Theory" of investing, inspired by Michael Mauboussin. This theory posits that the rise of passive investing has weeded out bad and mediocre managers, leaving only the strongest and most skilled players at the table to compete. Consequently, active management is becoming harder not because managers' skills are deteriorating, but because the remaining competition is smarter and more intense, leaving fewer easy games to exploit.