Depending on how you want to share your work, either having it just as a hobby (like wordpress, wattpad, fanfiction.net, etc.) or being published fo-realz, writing can be stressful. It's like someone has given you a block of concrete and it is your job or hobby to crack it open for a small ounce of gold contained within. Depending on how one does it, if you have the proper tools and experience or if you just hit your head against it long enough, it is still a difficult task. It is said that anyone with a basic grasp of language can write, but not everyone can write well. Unless you're some sort of genius like Harper Lee, you will have to practice a lot in order to forge your tools. And in the process, it can be frustrating to not know how to put that awesome story in your head down on paper. But the more you write, the easier it can become. That scene that once took you two hours to wrap your head around can now be written in a breath and you can now worry about on the next scene.
So in some ways, writing is one of the most stressful occupations out there, but at the same time the easiest. It all depends on how long you're willing to write in your lifetime without expecting pay or expecting anyone to read it, if at all.