Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of The Greenbrier Companies (NYSE:GBX) fell 12% today, after its ongoing saga with American Railcar Industries (NASDAQ:ARII), which also fell 10%, continued.

So what: The Carl Icahn-controlled American Railcar said it would bump up its offer for Greenbrier to $22 per share, still below what Greenbrier's board wants. Greenbrier came back and said it would buy American Railcar for a small premium. Both stocks are falling on the back and forth negotiations.  

Now what: Icahn has wanted to combine the companies for some time, and investors had been betting on a higher offer for Greenbrier; but even that doesn't seem like it will go through. The offer from American Railcar ends on Friday at 2:00 PM ET, so that's why the stock is down sharply today.

This is why betting on mergers is a tough business. Now that it appears that both sides are set against a merger, investors in both companies will lose out. Stay tuned to what happens next in this back and forth story.

Interested in more info on Greenbrier? Add it to your watchlist by clicking here.

Fool contributor Travis Hoium has no positions in the stocks mentioned above. You can follow Travis on Twitter at @FlushDrawFool, check out his personal stock holdings or follow his CAPS picks at TMFFlushDraw

The Motley Fool has no positions in the stocks mentioned above. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.