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NEW YORK (TheStreet) -- Today's selloff was totally rational, Jim Cramer told his Mad Money viewers Thursday. Investors need to strap themselves in because Friday could be another tough day as well.

What are the markets fretting about? Cramer ticked off the reasons. First, there's Friday's non-farm payroll report. The bulls are terrified of a strong number because that could certainly spark the Federal Reserve into raising interest rates. The Fed has been sending mixed signals as of late, calling rate hikes both inevitable but also data-driven, so what tomorrow's employment data really means is anyone's guess.

Next, there's Greece. What does a Greece-inspired meltdown really look like? The bears have many theories but no one really knows for sure. What the market needs is a resolution, any resolution, so investors can stop worrying and get on with it.

Lastly, the markets are worried about OPEC and whether Saudi Arabia will continue to keep oil prices low to stunt U.S. production growth. Low oil prices would be good news for some industries, like the airlines, but certainly not for the oil and energy-related stocks.

That's not to say good things can't happen tomorrow, Cramer concluded. We could receive a soft employment number, keeping the Fed at bay. There could be a resolution to Greece. And OPEC could signal a nice, slow move in oil prices. Any of those events would be met with a rally, as the markets often tend to rally once big, bad events finally happen.

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