AFP

Stocks keep notching all-time highs, but investors arent sure if thats reason to celebrate their riches or to hunker down and prepare for the party to end.

Anyone who keeps worrying that the markets impressive run is about to peter out keeps missing out on gains. So, the pile-on continues as the market keeps slowly-but-steadily pushing to unseen heights. Bull market psychology is controlling the day, says Michael Farr of Farr Miller & Washington. We discount bad news and embrace all good news.

Talk about a party that never seems to quit. The Dow Jones industrial average and Standard & Poors 500 jumped Friday to notch new all-time highs, while the Nasdaq composite set a 14-year high. The Dow is closed Friday at 16,947, just 53 points or a good day away from hitting 17,000. While the day-to-day gains are relatively small, theyre adding up to a powerful rally. The broad S&P 500 is up 6.2%, putting it on pace to post another good year.

Investors want to stay bullish about the market because:

* Policymakers are supporting the run. Investors took the testimony from Federal Reserve Chair Janet Yellen as an alls clear sign, Farr says. Yellen suggested last week that stocks are not particularly overvalued and indicated the Fed is standing ready to stoke the economy if needed. That encourages investors to own stocks, Farr says. The Fed is the wind at our backs.

* Sitting out isnt an option. Moves by central banks around the world make it costly to not be involved in stocks, says Doug Sandler of Riverfront Investment Group. With interest rates low and an uptick inflation a possibility, holding cash is one way that appears to be a loser no matter what. Investors recognize the penalty from sitting on the sidelines, Sandler says. What can go right for you on the sidelines?

* Earnings support the rally. If stocks were rising without underlying profit power from companies, investors would get more concerned, Sandler says. Companies are expected to post nearly 7% earnings growth in the current second quarter, says S&P Capital IQ. Thats more than double the earnings growth of the first quarter, and a powerful signal since corporate earnings are already at record levels. This is still a market with a reasonable amount of upside, Sandler says.

There are worries. If the situation in Iraq keeps oil prices elevated that could be an economic headwind for the market to overcome, Farr says. Though the Fed hasnt indicated it would, if it sets a deadline for taking its foot off the gas and sticks with it even if the economy isnt ready, stocks could suffer, Sandler says.

But for now, investors are enjoying an  impressive run some dont see winding down anytime soon. Everyone wants to be nervous, Sandler says. But we cant find a reason.