The first words are the hardest.
When the research is more or less complete and I have lived with my characters in my head for a few months, the day arrives when it is time to start writing. Once the new Word document is set up I can be tempted to follow many diversions and distractions: a fresh cup of tea, a quick walk to clear my head, feed the cats......and so it goes on. There is something both wonderful and terrifying about writing the first word, the first sentence, the first chapter.
I have just written 3,500 words almost without looking up and closed the document without even reading it through. I always make it a rule that I leave the work for a night before looking at it in detail. When tomorrow comes I may like it or not, change some of it almost certainly, add to it and expand it but for now I am quietly pleased that the first words are written. They truly are the hardest to write.