Cause of misjudgment № 19
Use-It-or-Lose-It Tendency
Skills and knowledge fade without practice, so the antidote is lifelong, deliberate use of what you've learned.
Mental skills are like physical ones: rarely used, they atrophy. Knowledge you do not regularly exercise gets rusty and eventually disappears. Munger treated this as a plain fact of how the brain works and drew a demanding conclusion — that a thinking person has to keep using the full range of their mental models throughout life, or watch them decay one by one.
The everyday illustration is the language or the calculus you learned in school and then never touched. Within a few years it is mostly gone, and you would have to relearn it nearly from scratch. The same happens to professional skills that fall out of daily use. By contrast, the doctor or pilot who practices constantly stays sharp, and the difference is not talent but exercise.
Munger’s prescription followed directly from the diagnosis. Keep your important models in active use by deliberately applying them, even to problems where a quick shortcut would do, because the practice is what keeps the tool available when you genuinely need it. He also argued for over-learning the most important ideas to the point of fluency, so that they are held more robustly and degrade more slowly. The whole “learning machine” ideal — going to bed a little wiser each night — depends on continuous use, not one-time acquisition.
