811.370 Failure to drive within lane; penalty. (1) A person commits the offense of failure to drive within a lane if the person is operating a vehicle upon a roadway that is divided into two or more clearly marked lanes for traffic and the driver does not: (a) Operate the vehicle as nearly as practicable entirely within a single lane; and (b) Refrain from moving from that lane until the driver has first made certain that the movement can be made with safety. (2) The offense described in this section, failure to drive within a lane, is a Class B traffic violation. [1983 c.338 §630]

a car is driving down a two-lane country highway, one lane in each direction. a horse jumps out into the road. the driver swerves left to avoid the horse, temporarily entering the other lane. is this person break law 811.370? if the answer is yes, does that mean the penalty must be applied? if that answer is no, then every situation must be taken in context. which means breaking the letter of the law is not enough to convict someone.

also, the entire body of law is too great for any one person to know. its an impossibility to know it all, so is ignorance of the law a defense? the judge in your case is also imperfect and will know a subset of the law. hopefully that judge will be knowledgeable of the area of law your case involves.

the applicability of the law also has to do with the will of the district attorney. it seems that the DA has great power in selectively enforcing the law. the complexity of human situations perhaps necessitates that in the end, the administration of law must be done by humans dealing in different shades of gray.