Obsessive I can do, big I struggle with.
Theoretically one (obsessive) should lead to the other without too many issues but big is scary. A large part is definitely fear of not finishing, the echoes of more abandoned projects than I care to admit to, and some which are ongoing over many years.
Like several others here I was diagnosed with ME/CFS about 8 years ago, I am very fortunate that I have made a significant recovery from my lowest ebb but I am still not functioning at 100% and have to pace myself carefully to avoid relapses. Quiet hand stitching is very therapeutic yet even so there is a limit to how much I can get done.
My other limitation is my 3.5 year old son, I can't disappear off to my studio much when he's at home with me but if I have some hand stitching he will (sometimes) let me do that while he makes Lego dinosaurs or watches tv. I have started tracking how much time I get to stitch and do art related stuff in a simplified bullet journal type system. Just ticking off 15 minute boxes here and there can seriously crank up the time and having a record is actually making me use the time I do have while he's at playgroup much more efficiently (lots less time wasted online)
My obsessive stitching this week is only 6x8 inches yet has taken approximately 8.5 hours of hand stitching, I'm not the fastest stitcher in the world and I guestimate time based on an average of 10 minutes per thread used.
I'm still deciding if it's finished or not so it's sitting on a wall for a day or two while I look at it and ponder. Now for a cup of tea and to read the next lesson.