Some people struggle the most with one particular aspect of writing and publishing, depending on what their individual challenges are, but . . . to be 100% honest? Every part is difficult in some way, even when you’re also enjoying yourself.
You can always look at this the opposite way (and I often do): view everything that’s behind you and in front of you as the hard part, but convince yourself that you’re currently doing the easy part. Tell yourself you’ll just breeze through this and the most difficult bits are either already done or a problem for another day. You’d be surprised how well this works!