This thread suggests that becoming a dad is not unlikely to throw you into a 2-year deep depression: https://news.ycombinator.com/item?id=30240609

"Even with this realization, there were lots of times where I sat on the couch the first year and just felt like I was drowning and life was over. That happened in the second year as well, but less after the child was 18 months. And by ~2.5, it's a lot better!"

That's hardly a good outcome for anyone, let alone someone who misses the joy of life they had in their 20s.