That the Torah would proscribe “placing a stumbling block before the blind (Leviticus 19:14) was so obvious to the rabbis that they saw in this a command for reaching ethical imperatives that range far from the literal text. After all, who could be so callous as to intentionally trip up the sightless?
Thus the rabbis teach: giving improper advice to someone who respects your opinion and could be lead to harm were your advice followed is tantamount to placing a stumbling block before the blind. Examples of this kind of unethical behavior are giving travel directions that involve traversing a dangerous road or deceiving someone in business by offering counsel to engage in a particular transaction from which the counselor would derive personal gain (Sifra, Kedoshim 35).
Failing to properly mark a grave so that a kohen would not defile himself by walking there is also a violation of “placing a stumbling block before the blind” (Mo’ed Katan 5a). Even a friendly act with honorable intent could be a violation of the law. Loaning money without witnesses, says a third century teacher Rav (Bava Metzia 75b), may tempt the borrower to renege on the loan. The notion of temptation (or its modern derivative, entrapment) is also an expression of the “stumbling block” prohibition. Thus, Rabbi Nathan rules (Pesahim 22b) that one may not place a cup of wine in front of a Nazirite (who has foresworn drinking wine, see Numbers 6) because the temptation may be too great and induce the Nazirite to violate the vow he would have otherwise observed.
Maimonides goes even further in applying the law. He prohibits the sale of arms and dangerous weapons to idolaters or criminals because once in their irresponsible hands, the weapons would be wrongfully used. Again, Maimonides rules, any action that would support the continued sinful activities of a Jew who is blinded by his own desires is also a violation of the law.
In today’s world characterized by an information explosion, the more we know the more we realize we don’t know. We rely on the knowledge, advice, and expertise of others. Others – similarly – rely on us. We are all, therefore, potential victims or victimizers, being mislead or misleading others. Our task is to remove “stumbling blocks” rather than planting them.