Writing was hardest for me when I had shitty reasons for why I wanted to do it. In me was an honest desire to be a good writer, but honesty is often mistaken for worthiness. My desires had been driven purely by the superficial, the vain. I was driven by a desire to be seen as important and insightful. To share myself because I found myself so interesting. But these are unsustainable reasons.
Because writing is such an arduous task, vanity can never be a sustainable fuel. Nobody should want to write, unless they were insane, not insane as comprehensively mentally insane, but madly plagued by some compulsion to express that is so strong that they must share it with others.
If sex weren't pleasurable then the obsession with it would evaporate. Without the pleasure -- physical and emotional -- most would lose their reason for engaging in such a sweaty, arduous task.
The same is with writing. The mechanics and process of it are actually painful or tedious -- take your pick -- and the only reason to do it is if there's an underlying message you are dying to share.
This might be taken rude by many on this site, but that hate will be worth it if this can convince even a single struggling person to ponder their honest and worthwhile reasons for wanting to write.
The reason why most struggle to write is because they are acting akin to someone having sex with a person they aren't attracted to, when they have no libido.
Just as software isn't about the literal code. And just as sex isn't about the literal physical friction. Or just as building a home is more than the literal hammering of a nail into wood and stacking of bricks. Writing is not about the literal writing/typing-of-keys. It's not even about the words or sentences.
It's about the message and what it does for someone who might read it.
So I implore you, if you are struggling to write, to take time and energy, and spend them on figuring out why at all you want to write. Just because it's culturally in vogue to be a good writer wont cut it. Be warm blooded. Get your reasons from within.