Since the market low in 2009, every move upward has been greeted with confident assertions that another crash was just around the corner.

After all, the world is still beset by problems, from the Eurozone, to China, to the gridlock and debt problems here in the U.S.

At some point, market gurus have assured us, this sucker's rally will end, and stocks will plunge.

Well, a crash is always possible, but as time goes by, a return to the 2009 lows seems less and less likely.

The Dow Jones Industrial Average (DJI) is up more than 110% from its 2009 lows. Despite some modest pullbacks along the way, this push higher has been steady and strong.

This year, the Dow is already up 10%, and it has set new all-time records in each of the past five days.

So, what's next?

Will the bull run continue?

Or will we finally get the crash that some investors have been waiting to use as an entry point for the past four years?

As ever, it's impossible to say.

Yahoo! Finance Senior Columnist Michael Santoli says those waiting for a crash may be waiting for Godot. The more likely event is a pullback at some point. If we do get that pullback, it won't be obvious that it's a "buying opportunity." It will look like the beginning of a crash.

From a shorter-term perspective, strategists like Goldman's Jim O'Neill have begun to worry about investors "selling in May and going away," a pattern that could leave us with the pullback.

In the meantime, although stock prices are high relative to cyclically adjusted earnings, stocks still look like a good long-term investment relative to bonds, which have yields that are so low that they have become quite risky. (If interest rates rise, which they seem likely to at some point, bond values will get hit.) And the U.S. economy finally seems to be gathering some steam.

So, as ever, the bull and bear cases balance out.

In fact, if we have learned anything in the last five years, it's that long-term investors should stop worrying about near-term market moves and just stay diversified.

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