Most strategies have a finite "capacity" and if you attempt to invest more than this, the returns dry up. So if you have lots of assets to invest you start to b

Most strategies have a finite "capacity" and if you attempt to invest more than this, the returns dry up. So if you have lots of assets to invest you start to be forced to invest in your 10th, 100th, 200th best idea, rather than just your top 1-5 best ideas. This is why it's very hard to sustain performance as funds grow. The reason people with big funds are focussed on growing their assets under management is they get an annual fee for assets under management, and this is therefore more reliable than the "outperformance" fee that they also charge.