Second-Order thinking is the ability to think about the second, third and nth-order consequence of a decision. Howard Marks describes second-order thinking in his book The Most Important Thing as:
First-level thinking is simplistic and superficial, and just about everyone can do it (a bad sign for anything involving an attempt at superiority). All the first-level thinker needs is an opinion about the future, as in “The outlook for the company is favorable, meaning the stock will go up.” Second-level thinking is deep, complex and convoluted.
Practitioners of Second-Order thinkers ask themselves the question "And then what?" a-lot. They think in terms of interactions and time, understanding that despite our intentions most interventions often cause harm. One could choose to eat a greasy hamburger each night. That solves the immediate hunger, but has a negative consequence on the long term.
Farnam Street recommends the following to improve your ability to think: