As the year approaches its finale, money managers are celebrating their triumphs (and minimizing any failures). The good news is that there's ample opportunity for emphasizing the former. Barring a year-end surprise, US stocks and bonds in particular are on track to end 2014 with solid gains. Wall Street won't be shy in taking most if not all of the credit for juicing the value of client portfolios. But let's take a minute and recognize the primary source for the gains over the past year: economic growth

Genius has been a bull market in 2014 and the critical factor behind this ascent has been a familiar influence in recent years: a rising economic tide in the US. Saying so isn't free of controversy, in part because more than a trivial degree of the positive macro trend is bound up with the surfeit of liquidity that's been engineered in central banks around the world. By some accounts, the economic expansion in the US is artificial, courtesy of the Federal Reserve's monetary machinations. Maybe so, but a synthetically powered expansion is just as profitable (if not more so) than one that arises organically.

Accordingly, let us give thanks to the main source of holiday cheer that accompanies year-end performance statements these days: the economy. The bullish macro trend in the US may be unloved, but celebrated or not the economy is responsible for the abundance of plus signs in US-centric year-to-date portfolio updates.

In the search for reasons why your investment strategy was successful, the US macro factor surely casts a long and, for now, positive influence. Financial economists have identified dozens if not hundreds of factors for deconstructing risk premia. But the leading factor is still the economy, and that's not going to change in 2015.

If you could know only thing about the year ahead in the cause of enhancing the quality of portfolio decisions, what would you choose? History strongly recommends the mother of all known risk factors: the business cycle. The economy's capacity for steering clear of recession, or not, dictates portfolio outcomes to a large degree, even if our egos have a tendency to assign credit for investment success to other sources. Mr. Market may be irrational at times, but he's crazy like a fox when it comes to favoring economic growth–and running for cover when the business cycle slides over to the dark side.