Confidence is everything, and for whatever reason, it's shattered at the moment. Being a hyper-competitive player like Gose -- and a star prospect all the way up the ladder -- it's a very scary thing when the thought finally dawns on you that you might stall out at AAA and never really make it. He's putting a lot of pressure on himself right now, and that's a pretty hard way to excel.
If you want to look at the bright side, his K/BB in his brief MLB stint this year was quite encouraging. He still has a future as a nice 4th OF at the very least, with a pretty decent shot at having some 3-4 WAR seasons IMO. There's no reason to think that he won't make an appearance in the bigs again this year, in September at least. All it really takes is a few multi-hit games to get his confidence going. The swing and miss will always be there, but the plus speed and CF defence are in no danger of declining any time soon; there are still a lot of useful things this guy can do between the lines when his head is screwed on right.