Of course, it might only work once. Well Every new idea, every old training gem, everything will work. Matching your personal goals to everything you come across may be difficult. No, it is impossible. One needs to learn the skill of discerning what is going to help and what is going to hinder.
Days can be bad, weeks can be worse, expect a dip or two each month.
I find a bad workout every two weeks, often just because of my job, the commute, or the weather. Because I keep a journal. No training program is more valuable than your own personal history. I am amazed with the gems that I find reviewing old journals. Three days a week works for me better than six, two better than four.