|Art Gerhard Nesvadba|
''....when you forget a bundle in the field...'' [Ki Teitzei 24:19]
Why should a person be blessed for performing a mitzvah if he unwittingly - and even unwillingly - drops money on the floor, which is later found by a poor person? [see Rashi v.19]
Chassidic thought explains that every Jew, regardless of his status and station, is essentially willing to do all that he is commanded to do by our Torah. The fact that he might sometimes be influenced to do otherwise is because his conscious state can be affected by external pressures that induce states of mind and even behaviour which is contrary to his essential nature [Rambam, Laws of Divorce 2:20]
Therefore, if he performs a mitzvah which was not consciously intended, it is nevertheless an act that is consistent with his inner, subconscious desire. In fact, what has actually occurred here is that his subconscious mind has been able to influence his actions directly, without passing through the conscious state.
So, if a person drops money which is later found by a poor person, he has done an action which is commensurate with his true, inner desire to serve G-d, and therefore he is blessed because of it.
Based on Sefer Hama'amarim Mehukat vol 5 p 50 Lubavitcher Rebbe