Most people stop thinking at the first consequence. “If I do X, then Y will happen.” Full stop.
Second-order thinking asks: “Then what happens?” You get the promotion—then what? You move cities—then what? You quit your job—then what? You start the project—then what?
The first consequence is usually obvious. The second consequence is where the real information lives. The third consequence reveals whether your decision actually makes sense.
Here’s the simple practice: Take any decision you’re considering. Write down the first consequence. Then ask “then what?” three times. If you can’t get past the second “then what?” without encountering a problem, you probably haven’t thought it through.
The answers you find at layer three are worth the effort.