Here is an image of part of a black corn cob.

The following image shows three rows of seeds stripped out of the cob and the arrow directions indicate the easiest direction to strip the next row.

The 100 planes on a diamond is like the stripped rows on a corn cob. Cutting perpendicular to the 100 plane when in the proximity of a 110 plane and linear to one of the two 100 planes when in the proximity of the third 100 plane.

So there you have it. Go and cut your diamond! But be warned, to become really proficient in this field of expertise you would need to put in the hours. Here I would like to quote Malcolm Gladwell The 10,000 hours principle comes into play – ouch!