First of all, if your dream game is something small like Flappy Bird, then I would say just go for it. But for most people, when you talk about a dream game, it’s usually something big and something that will take a lot of time to build. And when I say a lot of time, it usually means a year or even more.
It’s very hard to resist the urge to start building something you really want, but trust me, it’s a mistake if you haven’t got a lot of experience. At least it shouldn’t be your first project.
What usually happens when you’re aiming to high is that you start of with a lot of ideas, you work like crazy and then after a while you will probably realize that your dream game requires a LOT of work. But it is your dream game, so you keep working on it. A while after that, you can get buried with work, too many things has to be done, you have to learn a lot of new things and maybe it’s not even possible to build the way you wanted it to. And this leads to you getting burnt out or just simply losing motivation to build more or learn more.
So what should you do? Try to build small games. Get used to the idea of finishing things, and celebrate once you have done that. Get some experience under your belt. I’m not saying that it’s impossible to build your dream game as your first game, but it’s usually too big to handle. If you build a few small games first, get some feedback from other people and similar, you might discover weaknesses and similar in your ideas. By building stuff, you get better at programming, design and similar. And you will get a better understanding of the different parts of game development. This will hopefully make it easier for you to build the game of your dreams!