Adding Spigots

Imagine a barrel of wine that has one spigot, and thus only allows a limited flow. If one were to add more spigots, it would not increase the total amount of wine contained in the barrel. Rather, it would merely serve to let the existing wine pour faster. There is nothing one can do to add to the wine in the barrel.

The same is true regarding one's livelihood. Perhaps a person thinks he can increase his income by working longer hours. In reality, however, all he will "accomplish" by this is to decrease his spiritual merits, for by increasing his working hours he will automatically decrease the amount of time he devotes to spiritual pursuits. He will lessen the amount of time he devotes to Torah study, speed up his davening, or forgo davening with a minyan. As for the apparent increase in wealth that he perceives, it is actually an illusion. Hashem will see to it that he will lose all to an expenditure that would not have incurred otherwise, such as a doctor's bill or repair of property damage, or worst of all - that he received this increase at the expense of his portion in the World to Come.

(Chofetz Chaim)