This rings true. More specifically in my particular case, depression has already overthrown my life. I have the raw knowledge to manage it on a certain level, but depression itself undermines my ability to apply that knowledge.
I don't know how common it is, but your description is consistent with some percentage of presentations of clinical depression.

Here's what I think helps me function on my minimal level:

• Take my meds consistently (I need help for this)
• Visit my psychiatrist/therapist regularly (someone drives me to these appointments)
• Get the best sleep possible
• When I have the energy to attempt tasks, I try not to increase the mental-emotional difficulty of those tasks by attempting to be efficient; i.e. forget efficiency