"The flame that burns twice as bright burns half as long."

So cognitive enhancement is a thing.  There is literally a common drug in pill form that works akin to the fictitious NZT-48 from Limitless, at least for me.  I get it from my local pharmacy in 10mg and 5mg pills.  By the hundreds.  For cheap.  Covered by insurance.  It's called hydrocortisone, and (for me) it serves a medically necessary purpose by providing the cortisol my body no longer produces in sufficient quantities.  Like its fictitious counterpart, it comes with serious, long-term health consequences.  One unintended side effect is significant cognitive enhancement.

Describing cognitive enhancement to anyone who hasn't experienced it presents the challenge of describing a subjective experience to which not everyone can relate:

Like illustrating the difference between two shades of green only discernible to tetrachromats.

Like trying to get an energetic toddler to understand chronic fatigue.

Like describing depression to one who thinks of it as synonymous with sadness. 

I'll go with simple and (hopefully) relatable metaphors: speed and strength.

Hydrocortisone (in sufficient quantity) makes me mentally faster and stronger.  If my daily tasks are stones, with the help of HC I can throw ten in the time it took me to throw one.  Or, I can throw one with only a tenth of the effort.  That's cool, but so what if I can throw stones faster and easier?  The tasks get done either way, right?  Wrong.

Some mental tasks are time dependent.  They only get accomplished successfully if one can complete them within a certain amount of time.  For example, noticing heavy traffic on the highway ahead, with ~20 seconds to decide whether to take the nearby off-ramp and a completely different route.  On HC, it is easy for me to make this decision, because I can quickly plan a new candidate route and estimate the time time it would take, even without total familiarity of the roads involved.  Another time-dependent task is wit.  Being witty is something that usually has to be done within a relatively short time, or the moment is gone.  Without HC, the act of thinking resembles wading through water, instead of walking (or running) on dry land.

Mental "strength" factors in because some difficult tasks cannot be subdivided and tackled piecemeal.  These are like boulders.  Either I am strong enough to handle them, or I'm not.  Just as no amount of time or willpower would let me lift a large boulder, no amount of determination would help me tackle difficult problems and concepts.  So it goes with cognitive enhancement via HC.  In Dungeons & Dragons speak: +5 INT per 5mg pill.

So, what's the point of tossing stones and hurling boulders?  Fighting giants, of course.  Let me go ahead and preempt the obvious David and Goliath remark -- this isn't a perfect metaphor.  It just serves to illustrate my point.  

Yes, taking hydrocortisone will likely cause me significant health problems, but there's not much I can do about that, given that adrenal insufficiency puts me in the hospital.  Of course I'll do what I can to wean off it as much as possible, but while the hydrocortisone high is there, I'll be riding it with a smile.  If I lose the cognitive benefits as I wean off, then maybe I'll have some interesting decisions to make.  Such as:

Is it better to burn out, or fade away?