Fitness buffs know the importance of working out, stretching, and training to maintain or improve their form.  They dedicate untold amounts of time to this activity and the results are noticeable.  On the flip side, if you stop working out, or never start in the first place, the results are noticeable in that case, too.  Muscles that lack definition, agility, and strength appear different than those that are cut, trim, and firm. 

The learning muscle, the brain, is just like any other muscle in body.  While it's not technically defined as such, it requires training, flexing, and stretching if it is going to develop to its full potential.  When the brain is only presented with what it is already capable of determining, there is no work out.  However, when the brain is presented with a challenge, the muscle flexes, then is stretched, and finally begins to the show the cut and trim lines that will define it.

Just like the body, you can't expect the learning muscle to spontaneously develop.  It requires effort, some discomfort, and energy.  You can expect to be tired after a mental work out.  But, the rewards are worth it.  Sometimes, like with the physical body, it may be necessary to employ a personal trainer, someone who can help you expand your intellectual work out.