But he gave a thought to leave chocolate and take Salad. How do you think this got triggered in his brain. Discipline comes after you have formed rules by seeing it's effect either by you or learning from others.

Second-order thinking is too abstract: some time thing which is obvious for you might not be for other e.g. binary search is not always a good option, it can be obvious to you (here you are an intelligent person with acquired knowledge) and for novice to this concept; their second order thinking would be to find out what Binary Search is and then why not it is always good to use it.

I think second order is trying to convey to look beyond what you have good in your first glimpse and try to connect dots. I haven't done much study on it but that what I get from it.