I have had this question since before I can remember. You might even call this question one of the great mysteries of the world.
First, I have to set the stage for this question so you will get the full effect.
Picture yourself coming home form work, school or maybe even when you first wake up. You head straight for the kitchen looking for a tasty snack. Naturally you bypass the bowl of fruit and head for the cookie cupboard. As you open the door, you see the package of Oreos has been opened and to your astonishment the previous patron did not close the package. Instead the cookies were left to the elements. Your heart begins to race as you hope you are not too late. As you sink your teeth into the first cookie you can grab, you realize with horror that you are too late. The cookie that is meant to be crunchy is now soft and oh yes, even mushy!
To fully understand this mystery there is another similar scenario except instead of reaching for a crunchy Oreo you reach for a chewy, Soft Batch Chocolate Chip cookie. The package also left unsealed, cookies exposed. The first cookie you eat is not a little bite of soft, chewy heaven, but a tough, crispy disappointment.
So, to sum it up. When exposed to the elements, soft chewy cookies become hard and crunchy cookies become soft. In the name of all that is holy, why don't they just get harder or just get softer. I have spent many sleepless night wondering why, WHY! I can only hope that some bright, budding scientist is poised to explain this so far, unexplainable mystery. So if any of you out there happen to know the answer please let me know. In the meant time, please keep those cookie bags closed and those cookies preserved.