请各位大虾帮我分析一下，文献“investor sentiment and the Cross-section of stock returns”中，出现了这样一段话" Because a mispricing is the result of an uninformed demand shock in the presence of a binding arbitrage constraint, we predict that a broad-based wave of sentiment has cross-sectional effects (that is, does not simply raise or lower all prices equally) when sentiment-based demands or arbitrage constraints vary across stocks. In practice, these two distinct channels lead to quite similar predictions because stocks that are likely to be most sensitive to speculative demand, those with highly subjective valuations, also tend to be the riskiest and costliest to arbitrage. Concretely, then, theory suggests two distinct channels through which the shares of certain firms—newer, smaller, more volatile, unprofitable, non-dividend paying, distressed or with extreme growth potential, and firms with analogouus characteristics—are likely to be more affected by shifts in investor sentiment.”
我实在不太明白。为什么套利会受到约束，什么情况下套利会“最有风险和最昂贵”？如果说是因为一些股票的定价受主观判断的影响而难以确定真实的价格，所以会出现难以套利的情况，那么套利和情绪不就是一个东西了吗？文中后面得出的关于情绪影响报酬的结论，并没有排除难以套利而影响报酬的因素阿。实在不明白，求解。