Writers block is the most lamented problems writers have, at least on the internet. It’s often defined as when a writer can’t keep writing, the idea’s just won’t come or has a mental block or something poetic like that.
Honestly I think many people over state it, they think that because writing is art it can’t be forced or understood.
If your having writing block odds are its one of a few things that are really the problem.
First if could be you did not really think out what your doing well enough.
The worst two weeks of writing I had was when I was planning out a set of scenes, nothing worked. It felt like quicksand, I would make a little progress then it would just fill back in. However the problem I had was that I had no good reason to have the main character do anything interesting during the scenes. The only logical thing for him to do was to hide in a closet and let the marines handle the situation, I was trying to shoe horn him and the entire situation, that was why nothing worked. The solution was to cut the entire part out and work around it.
Second it could be you have not broken down the problem enough. Like everything else in life writing is about solving problems. Most problems can not be solved as they are, you have to break then down.
For example one problem I had in my fourth draft was that I needed to detail how the relationship between the two main characters started better.
Instead of just trying to hop right in and start writing I wrote the three abstract things I wanted to do. Then under each one I wrote practical things, like “Have a scene where they do [X] together”. This made it into something I can understand and do.
Lastly, because you don’t have anyone breathing down your neck to finish you have no or little pressure to make progress. This can mean that you keep looking for the perfect solution to everything.
There are several problems with this, first you often will only find that answer when your writing, not planning. Many many things have changed in my book because of idea’s I had when writing, things I could have thought of when planning but never would.
You also need to accept that some problems have no good solutions. For example in the Martian, the most hard sci-fi book I have ever read, the sand storm that starts everything is VERY unrealistic. However Weir could not think of another way to set his book up so he kept it.
Sometimes you have to accept bad answers and hope your readers forgive you.