What actually happened was that I changed my mind about my blog posts all the time. T was going to be about Talent not Totalitarianism, U was going to be about Universality not Unicorns, Y was going to be about Youth not Yippedee-doo-dah. Perhaps the A-Z would have been better for sticking to the initial list I scribbled down in 5 minutes, but I think not. They were a bit obvious and boring. Well, they seemed obvious and boring to me, which didn't bode well given I was the one who was going to write them.
I'm the same with planning what I'm going to writer my novels. I can plan with the best of them - in fact, I can think of nothing nicer than spending several days faffing around with index cards - but when it comes to actually writing material to flesh out my plan I zoom off piste pretty quickly. The only time I've tried to stick to The Plan I got so bored I gave up.
For me, the planning comes best AFTER I've written a first draft, not BEFORE. I use the index cards to whip that stodgy wodge of material into a decent shape. This may involve lots of new writing, but that seems to work as I've already got a reasonable framework down on the page.
Some people need the plan first to anchor them and provide security. I believe Ken Follett does such detailed synopses of his books that it really is only a matter of fleshing them out a little. Each to their own.
I know that I need to have at least something down on the page before I start planning, but the further I have written into the novel, the more detailed my plan becomes. The plan and the story grow organically together. But that's my method: it may not be yours.
Part of the process of becoming a writer is to work out what works best for you. Maybe you're a planner, maybe you prefer sailing into the mist. Be open minded, try both, and learn from the experience. Keep learning. That's all you can do.