What is the purpose of each one?
Bullet Journal: organize tasks, events and notes in structured system. It has an index, coding, calendars. Optimizes productivity and memory.
Artist's Path: drain unfiltered mental content. Without structure, without objective, without system. Optimizes creativity and self-knowledge.
Why does mixing them kill both?
The BuJo is structure; the pages are chaos. If you try to structure your morning pages, you kill them — you lose the free flow. If you try to make free pages in your BuJo, you mess up the organization system.
Cameron is clear: separate notebooks. One for BuJo, one for pages. Don't confuse them.
Do they complement each other?
Yes, very good. People who keep both use the typical pattern: morning pages at 7am (separate A5 notebook), Bullet Journal at 8am (BuJo notebook), start the day.
The pages drain noise. The BuJo orders the day. They work in sequence, not mixed.
Which one to choose if you can only keep one?
It depends on your bottleneck. If your problem is task/schedule chaos: BuJo. If your problem is creative block or mental noise: pages.
If you have both problems and can only handle one, start with morning pages for 12 weeks. BuJo is learned quickly; Pages take time to work.