Really?!?  Seriously?!?  Is laziness or half-hearted effort REALLY as bad as someone taking a sledge-hammer to the machinery?!?  This seems like craziness to me...

The thermodynamic principles of entropy and equilibrium seem to back up this Proverb, however.  These terms basically refer to the process of energy distribution, natural systems moving from order to disorder -- and it seems to bear up in real life.  Left to their own devices, many things automatically revert to chaos and disintegration.  Consider lawns, kindergarten classrooms, marriages, factories, social groups, and a thousand other potential examples.  It really seems true that ambivalence or apathy leads to destruction.  They really are brother-concepts.

It's a good challenge for life -- and it can be applied to many areas of existence, not just work / employment.  Consider the statement, "One who is slack in his marriage is brother to one who divorces."  Or "One who is slack in his spiritual life is brother to one who drifts away from God."  Or "One who is slack in his parenthood is brother to one who establishes generational patterns of dysfunction."  It seems like the proverbial statement really could work on multiple levels.  "One who is slack in his ____________ is brother to one who _____________ (insert the specific form of destruction)."  Are you slacking in any area of life?  Do you need to consider the implications of this for the future in any way?  One who is slack in thinking about these things is brother to one who unknowingly gets himself into trouble down the road...