I'm...gonna be kinda harsh here, mostly because I needed someone to shake this out of me when I was struggling with writers block.
Writer's block is a cop-out. It's a phrase used to mask the underlying problems you're actually facing: Fear and Insecurity.
Tackling your own fears and insecurities are terrifying, but if we call it writers block then suddenly it's not as scary. But that doesn't make the effects of that fear and insecurity stop. And the thing is that fear and insecurity stems from different wells depending on the creator. For some it's a fear of success, for others it's a fear of rejection or a fear of failure all of which can lead to a lack of motivation.
To tackle this problem entire depends on what mixture of fears and insecurities are whirling around in your head. Unfortunately, I've had to deal with ALL of them.
Fear of Failure is created by an excess of perfectionism and constant self-criticism.
Fear of Rejection is created by putting what other peoples opinions about your work above your own.
Fear of Success is created by a worry about what happens to others if you become successful.
The Lack of Motivation that all of these accumulate into what we call Burn Out.
A lot of folks in creative industries go into it unaware that your creativity is a muscle. It gets TIRED. It needs to rest. If you're struggling to work on your own project after spending weeks hauling butt on another, you need to stop. Constantly working isn't helping anyone, and it can actually lead to a lot of interpersonal problems down the road. Start keeping track of when you're getting distracted, having a hard time focusing or struggling to produce simple things. Have you taken care of yourself? Have you had a shower? Eaten? Had some exercise? Have you socialized with people? These are things you HAVE to do in order to function as a human being. If you're not addressing your basic human needs then how can you create anything?
I've had to combat all of this personally I had to step back, and reassess my own expectations of myself. For example, when I was frozen in fear writing a novel, my therapist said: Why not write...a kids book? I thought she was nuts. A kids book wasn't what I wanted to write. And that was her point. Work on something you KNOW you can succeed at. If I didn't want to do a kids book I could write a research paper on something I knew about or wanted to learn about. I ended up writing a little poem about fish that I plan on making into a baby book one day. Is it something I'm ProudTM of? Eh. Did it kickstart my creativity? YES.
TL;DR - Writers block is a hydra of fear, perfectionism and insecurities masking itself as something safer than what it really is. It's BS. Call it for what it is, and then start tackling the problem.