How do you deal with the, “Grass is Always Greener,” syndrome in the Army?

I know what you mean. I've felt like that in the past, but haven't felt like that in a very long time after "realizing" two things ("realizing" being in quotes because we all know these things, but it's not always at the front of our minds):
1) Nobody in the Army is useless. Basic Training wasn't that difficult to us probably, but the process for joining at all is decently exclusive, and once you look around at a lot of the general public our age (I'm assuming we're around the same age, I enlisted at 18 in 2016), you might realize we're definitely doing something a vast majority of them couldn't. I'm not trying to downplay civilians, some of them couldn't get past MEPS or BCT for reasons they might have 0 control over, and at least they tried. My point is, you're doing something most people aren't able to do for an organization most of them can't be a part of. In reference to the "Grass is greener" problem, consider not even being there at all.
2) You might feel stagnant at the moment, or like you're not doing much, but that just means you're given time to better yourself physically and mentally and prepare for literally whatever it is you want to do with your career. If you don't like where you're at, start using this time to prepare for something bigger. Just keep it in you're head you're working toward SOMETHING.

Sorry for the wall of text, I just know what you might be feeling and thought I'd give the most I could on how I dealt with it.

Send your dog over to pee on their lawn

SGT (Join to see) In 1953, I was at Ft Knox, in wooden barracks near Godman Airfield.

The unit bulletin board had a notice that Soldiers were needed or Airborne Training! I was not fat, but dumb and lazy! I did not apply - that Army, 1953, did not provide much guidance.

Open your eyes, look around, check on ? the net. Get gone and enjoy, You might have to volunteer - so what !