It goes without saying that a mutual fund represents management's "best ideas." No one would ever invest in a fund without believing management was putting forth its top investment strategies.

So when Northern Trust funds recently sent out a notice touting the Northern Global Tactical Asset Allocation (BBALX)fund as representative of the company's "best investment thinking," it was hard to read without laughing.

The pitch brought to mind the ill-fated Morgan Stanley Dean Witter Competitive Edge "Best Ideas" Portfolio, which became an industry laughingstock in the late 1990s. The fund drew limited interest, provided mediocre (at best) results and elicited jeers from analysts before being quietly liquidated and mostly forgotten.

That would be true of any fund company that runs multiple funds and is foolish enough to single out one issue as representing its best ideas. But now that Northern Trust has stepped into the fray, the company is at the center of a lesson in the difference between what funds are selling and what investors need and ultimately get.

Last August, Northern Global Tactical Asset Allocation went from being a fund for institutional investors (with a $5 million minimum initial investment) to one that ordinary consumers could buy into for as little as $250, giving Joe Average access to the firm's "Investment Policy Committee."

This committee, which includes the company's chief investment officer, its chief investment strategist, the head of active equity and the head of fixed income, evaluates data such as inflation trends, credit spreads and currency movements. It then mixes in earnings growth and valuations to come up with a tactical asset allocation plan, which guides investment decisions across stocks, bonds, cash and alternative investments. The company implements this by investing in other Northern Trust funds and some exchange-traded funds.

When Northern Trust contacted me about Global Tactical Asset Allocation in late October, the fund carried a four-star rating from investment researcher Morningstar. That has since been cut to three stars. The fund has a below-average expense ratio and a track record that puts it ahead of the average "moderate allocation fund" on year-to-date, one- and five-year time horizons.

Certainly, investors could do worse. But does this product really reflect the company's best investment thinking?

The minute a company uses such language it starts raising red flags, because it comes close to invalidating the rest of its own efforts (which, in this case, include the funds in which Global Tactical Asset Allocation invests). Why buy any fund except for the one that represents management's best ideas?

Moreover, as Morgan Stanley Dean Witter found out with its Best Ideas portfolio, when your best doesn't produce great results, it brings everything into question.