The decision by Scandinavian fund manager Nordea Asset Management to turn new investors away from its blockbuster €19 billion multi-asset fund, following a period of breakneck growth, is a welcome one for investors. Arguably it's a step some other fund managers might want to take.

Capacity is the Achilles' heel of the successful fund manager. The better they do, the more investors throw their wallets their way. But the bigger a fund gets, the harder it is to find the overlooked gems and flashes of investment genius that propelled it to the top of the rankings.