I do not know if it is the hardest thing I have done, but I have a quilt partially put together that has been sitting in the UFO pile for quite a few years now.
It is a quilt that I started to hand quilt using the quilt-as-you-go method. It is waiting for the borders to be added. I discovered I absolutely detest the method. I would much rather put the whole top together and hand quilt it all at one time, rather than doing it in sections. I do not like the extra seams on the back. I do not like having to lay it out each time to sew strips together and then quilting in that area, then repeating the process to add the next partially quilted panel.
You get the idea.
Question, is it difficult, or is it really you do not care for the method?