An old thread was necro'ed and I saw this in it;

Man, I was so optimistic back in April, wasn't I? But then I realized that I made the most amateur of amateur mistakes: I wrote a story that would take five or six years to complete.
I'll probably be dead by then!
Well, I'm not that old. But I am old enough now that I can't take long term projects like seriously unless it's paying my rent. Vanity comics usually don't do that. I have been rewriting but it's not looking like I can shave the idea down thin enough to still make it work. It's better to focus on something more manageable.
I'm mostly just sharing/ venting here. But have any of you let enthusiasm blind you to practicalities? Tell me about it.