Lyric writing is way more difficult than writing music for it. I can come up with decent melody lines and chord arrangements. I can even hear harmony lines and drum patterns that work. But for me, lyrics are the hardest part. I'll come up with a really good chorus at times and stuggle to fill out the rest of the song. Other times the whole song comes to me at once. Other times I'll have a tap on some theme or idea but not be able to come up with any words to express it. I've heard that songwriting is 10% inspiration and 90% perspiration. To a large degree I think that's true.