Do not put an obstacle in front of a blind person (Leviticus 19:14)
Just as “deaf” in the previous mitzvah is understood metaphorically, so, too, “blind” in this mitzvah is not meant literally. (Well, it is meant literally, too, just not exclusively.) The meaning is not to place an obstacle before someone who is “blind” in a particular manner, in order to take advantage of his ignorance. The prototypical example, cited by Rashi on this verse, is not to advise someone to sell his field in order to buy a donkey when you’re secretly conspiring to acquire the field for yourself.
Also included in this mitzvah is not to cause someone to commit a sin, or to assist him in doing so. If you know better, you’ll be helping another to stumble in this matter.
It goes without saying that one can’t literally put a physical obstacle in the path of a blind person.
The basis for this mitzvah is clear: society depends on people being able to trust one another. If everyone is always looking over his shoulder expecting the other guy to stab him in the back, society would stagnate and wither, not grow. If someone relies upon us for guidance, we may not always give perfect advice. Nevertheless, there should be reasonable assurance that we aren’t misleading others because of ulterior motives.
This mitzvah applies to both men and women in all times and places. It is discussed in the Talmud in tractates Avodah Zarah (14a) and Baba Metzia (35b). It is codified in the Mishneh Torah in the twelfth chapter of Hilchos Rotzei’ach. This prohibition is #299 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #76 of the 194 negative mitzvos that can be fulfilled today as listed in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.