My sons are five years and eight months apart.
I was naive in thinking that I knew what I was doing the second time around. They were complete opposites to each other.
My oldest was a wonderful eater/sleeper, happy and I could take him anywhere and wasn't at all fussy.
The second child was always grumbling, a terrible sleeper and eater and just seemed much more unsettled.
For balance, the third (three years and four months from the second) was a great eater and sleeper and generally settled.
However, the oldest remained friendly with the years, the second one became a bit calmer but somewhat irritable and the third had a few years where I wondered if someone swapped my sweet little girl with a small monster when my back was turned at the store.
They're now adults and the oldest is extremely difficult. The middle child is very happy and pleasant and the youngest is very calm.
I suppose my life would have been easier had I just acknowledged that they are different people and what worked for one doesn't for another. That's pretty much it.