I didn't believe in writer's block until I experienced a creative block after a devastating illness and schedule disruptions stacked on one another last year. I was willing to write but became restless at the keyboard and couldn't focus. It was hard to get back in the groove.
This really devastated me, because my agent was waiting for a submission, but thankfully she understood, having seen this before in other writers.
The idea of having angst as a writer can seem glamorous, but to me it was a pain. I am normally quite disciplined and just wanted to meet my obligations. Looking back, I can see that my creative block was linked to my state of health. Once that corrected itself, I had no trouble slipping back into gear. Also, external forces can disrupt our focus for a time. When that happens, working to smooth life out will yield benefits.
I'm happy to say that I'm doing well now, but the experience marked me. For months afterwards, I was afraid to commit to a project schedule, in case I'd be unable to complete it.