Successful people in every field gather together.
They seek out people who do what they do and who can speak intelligently about their shared endeavor.
You can't do it alone
The criticism you receive from outside the writing community won't help you because your friends who aren't writers don't understand writing. They mean well, but they have no background, no experience, no knowledge, no training.
Your best friend says, "I don't get it." Your mother says, "I thought it was very nice, honey." Your co-worker says, "I laughed, I cried, you want to get a slice of pizza?"
You need professional criticism
Your best friend can't tell you that you have a brilliant first act, but with a few deft changes in the opening sequence you can make the reversal at the end of act two even more devastating.
Your mother can't tell you that your flashback on page two is evocative, but the action of your story would be better served if you got to the central conflict more quickly.
Your co-worker thinks poetry has to rhyme.
Simply put: you're working in a vacuum. You don't even know if you're improving. You're alone. You're going to go crazy.
You need to be in a community of writers
And there are other reasons to be part of a community. It can inspire you. It's fun. And it's just a fact—writers need each other. Writers need a forum in which to present their material, colleagues to encourage them when the initial inspiration fades, and a guiding hand to make it all work.
Gotham Writers' Workshop is that community.