That was exactly what I thought! I think it came from learning English in high school, I was always encouraged to just get anything down at the end to conclude my writing !
Now, I realise that the intro is vital to hook people in, and the conclusion is the final piece of encouragement to get the reader to feel like they want to clap / respond / engage / act upon what you’ve said.
For me, it varies. I am guilty of overthinking. Being honest, this one I wrote in one shot, in about 2 hours, and then maybe another of edits through a few friends. This is the way I am trying to go! If I start thinking too much, it can take me HOURS.