Life is not consistent. Let's face it, we have hormones. Sometimes, my kids are tired, sometimes, they are not. 

We are supposed to create security, respect for discipline and good expectations by being consistent, but when we get too rigid in the name of "consistency" the opposite can actually happen. 

For example, if you follow-through on a consequence that a child has worked really hard to make up for, and feels really bad about, keeping that consequence, or not even modifying it in any way, can be discouraging.

Or let's say you're really tired, and you have one of those children that won't take "no" for an answer. Not letting go, sometimes, can lead to major power struggles, and, if you are at all tired, can end up with you screaming. Hysterical screaming vs. inconsistency... hmmmm, I think I'll take loosening up.

The link to this article gets into more detail about it, so you don't end up backing down to avoid disciplining your kid every time. But it's time that we relax our standards and opt for sanity. Real life is not consistent - we shouldn't always be either.