How fast the extraordinary becomes routine. Swings of hundreds of points in the Dow Industrials, rarely seen for decades, are now so common that they barely merit comment even in the financial media. Since many Dow stocks are priced above 100, 200 and 300, small percentage moves in a few issues impact the Dow by hundreds of points. Do the market swings mean much? To a trader, yes. To a long-term investor, no.

The net effect of this "sound and fury" has been barely more than rounding error in a long bull market. I remain upbeat because investing is about earnings and interest rates. Not about today's economic numbers and not about presidential tweets, but about future earnings and rates.  Investors correctly anticipating significant changes position themselves long before better numbers appear. That explains the market's strength the past year. Investors have been seeing better days ahead. They were right.

Earnings are set to surge this year. Blackrock anticipates S&P earnings growth of 19 percent this year on the heels of rising optimism thanks in part to corporate tax reform. Other firms agree that the tax bill's positives are underestimated and underappreciated by investors, though not by businesses. Warren Buffett said the tax bill provides a "huge tailwind" for businesses.  I've been saying as much since it passed.

What can go wrong? First, for reasons that can't be anticipated (shocks of one sort or another) the GDP and earnings growth so many expect may not materialize. Things can happen. GDP growth much above three percent could be difficult to achieve due to demographic trends (the aging population) and a shortage of skilled labor. A lot has changed since the 1980s when growth topped 4 percent for years. 

Also, inflation could rise more than expected and with it real interest rates, the other key factor impacting stocks. By definition, higher interest rates undermine stock valuations -- the present value of the future earnings the bulls foresee. But if rates are rising because the economy is growing, then so will profits and stocks. 

Finally, rising demands for credit from the private sector in a growing economy and from Uncle Sam to finance budget deficits could push rates up. True enough, especially about Uncle Sam. I worry about this. But right now the credit markets and client income holdings do not reflect a real concern about rising rates. 

Bottom line: The real positives (GDP and earnings growth) will limit market sell-offs and, although volatile, the long-term bull market remains intact.