There are certain things that one should not do:
One should not knit with new yellow yarn when wearing black, unless one wants to be wearing black with yellow fuzz.
One should not double-knit with different thicknesses of yarn. Both yarns may seem to be worsted, but unless they are truly the same, there will be... complications.
One should not knit with new black yarn when wearing white (or khaki), unless one wants to be wearing white/khaki with black fuzz.
One should not go hat crazy with homework to do.
One should not write notes to oneself with Greek letters during Hebrew class.
One should not drink two smoothies in one day and not expect to have an increased restroom visit count.
One should not forget to rinse the violet-watering-baster after using said baster to put coffee into ice cube trays.*
One should not expect meetings to happen at their appointed date or time until the meeting has actually begun at said date or time.
One should not stare at the awesome beehive during Hebrew class.
One should not forget that yogurt that freezes is frozen yogurt.**
One should not forget to update one's blog.
*This one didn't actually happen, but nearly did.
**This is awesome.