The Medrash Tanchuma (#5) tells us that there are gifts a person may have, some of which remain with him for a long period of time, and some of which wither away after an unexpectedly short period of time. The Medrash tells us that there were two people – one Jewish and one Gentile – who were fabulously wealthy, but came to lose their wealth: Korach was the Jew and Haman was the gentile. Why was this so? The Medrash tells us it was because their wealth did not come from Hashem, but rather they grabbed that which was not designated for them. So too, the Medrash lists the tribes of Gad and Reuven as having great wealth, but then losing it while going into exile before the other 10 tribes.
I saw this Medrash explained using the following principle: We all have an obligation to make an effort (hishtadlus) in order to support ourselves. However, a person who over-works to generate greater wealth will eventually lose that which he has acquired, similar to a thief who will lose the possessions which he has stolen. We do not find anywhere in chazal that implies that Korach stole, nor that the tribes of Gad or Reuven became rich through any kind of illicit gain. We only find in this Medrash that they “grabbed” – becoming overly aggressive in their pursuit of parnassa. It seems that the Medrash is comparing “grabbing” to “stealing”, and this grabbing is what caused their eventual downfall.
There is a story told about the Kotzker Rebbe, who saw a man race out of shul before the end of the last Kaddish (barchu), grabbed his pushcart, and rushed off to sell his wares. The Rebbe asked him “Where are you going?” and the man answered, “to make my parnasa”. To that the Rebbe countered “how do you know that you are running to your parnasa? Maybe your parnasa is in the other direction and you are running away from it.” (meaning: maybe you would make more money by doing what a Jew is supposed to do (thereby gaining siyata dishmaya) and stay in synagogue until the end of shacharis, as opposed to trying to grab an opportunity, by leaving shul early which might not be good for you after all).
Typically, at this time of year, when we slow down from our normal parnassa pursuits, we seem to see hishtadlus as not as pressing as usual. Maybe we should see this as the standard of how much hishtadlus we should be doing during the rest of the year. In our spare time, when we use it properly (e.g. to spiritual pursuits that we have neglected during the rest of the year), we may find out that these spiritual pursuits may be counted by Hashem as hishtadlus itself!