Where does one draw the line between doing something extremely well and something pretty good?

How much time should we focus on the details — do the details comprise the whole?  Or it is comparable to the law of diminishing returns, where the more time one spends on something to attain perfection, the less ground one really gains?

And how should we cover the details on something that’s not our specialty?  In other words, how do we know they’re taken care of if we don’t know what we’re doing? 

Yep, this is all pretty nebulous.  Maybe you have some ideas.  Maybe you don’t.  But let’s just see how it all works out.