The inside enemy
Being positive is good for mental health and for life in general. It's a well known fact. However the production of a game can take time. Staying positive on the long run is very difficult, almost impossible for a lot of people.
The negative one can feel about her own project is almost always related to doubts about the quality, the feasibility, or the message. When you work on something for too long it's very easy to forget the awesome and only see what could have been better. Try to focus on what's essential: the big picture. There is no point in regretting a feature that has not been implemented in the end. Even if the taste is bitter, none of the players will taste it as they won't even know you ever planned to implement this feature you miss so much. They will take the game as you made it, not as you had one day planned to make it. It makes a big different of perspectives.
Remember to always see your game as it is, not as what it might have been.
The outside world
Internet is a great place, but Internet is full of mean people. One of the first rule you should learn in this industry is to not pay too much attention to comments.
If you take an article about an awesome game you love on a random site, you will always find some hate in the comment section going in the exact opposite direction of what you feel or think. It's something happening on a very wide scale and on topics way more important than video game development. On all topics it's pretty common that the ones who are the loudest are, in the end, the meanest ones. Because Internet anonymity offers a fake feeling of security they say all the dumb things they have on their mind, and they often do it without thinking that some fellow human beings could be hurt on the way.
Video game development is still seen as a mystical and magical activity where only some elite can live. A lot of people don't see the development of video game as an easy activity one can do alone or with a very small team. When they think only huge companies with no human faces can produce games it makes it very easy to insult everything about the games and the people who make them.
You can't avoid or prevent hate about what you do. Video game is (still) a creative activity and people may not share your taste. It's normal. What is not is to only take the bad and mean critics about your game and give them too much credit. Your game won't please every one, it's simply not possible. For you and your game sake you must only take what is relevant in the comment and critics, and don't over presume of your game qualities and strength.
Use only what you feel could make your game better. But don't use everything. Remember that you make a game for a lot of various people to play, not only the loudest ones. You are not born game designer, neither they are. You know your game better than anyone, you know where it will go, and what it should look like when the release date comes. Don't let others decide for you what should or should not be in your game. Take what you feel can make it a better thing, and let the rest where it belongs, in the belly of the grumpy Internet.
Even if it's hard, try to always be constructive with people's feedback. Try to understand if the point is justified or not and act accordingly. But, please, don't spend too much time reading thoughts and points about your game. It may lead you to even stop making your game at all. We all know game designers and game developers who had very harsh times dealing with critics. Use it for the better, but conscientiously.
If you really want to have a recurrent feed of information and feedback about your game, start a forum on your web site. In contrary to the articles and news comments, people registering to a game forum usually come to make it better, not just spit on it or its creators. Use a forum/question board/Reddit/anything relevant to gather players and talk about the game. However, you should also take care to avoid the over positive feedback. They are almost as dangerous for your sake as the negative ones.
Create a virtuous circle
To keep the pace with the game development and stay positive on the way it's important to create a virtuous circle. Talking about positive things or quoting positive feedback will, naturally, create more positive things and feedback. Use it for you, your mental health, your communication, your audience... everything. It's easy to become enthusiast for something when you realize most of the people are already very positive about it. The only important thing to keep in mind here is to be sure to not let people have fancy expectations about the game. You should always communicate about the positive truth but not let your future players imagine a game that is different of the one you're working on. Recent industry drama proved that when players have a biased ideas on what a game will be it can end dramatically for the team, the game, and the community. Always be positive but honest about everything and especially your game.
In the end
Making a game is difficult enough to try to avoid diving into an infinite hole of negativity. Always remember your game strengths, fit to your initial plan and use the positivity of your future players to release the best game possible.