You are ready to start a newsletter when you have one or both of these:
1. Social Capital or Digital Footprints
You need a decent personal brand that acts as your ToFu, or you should be super active in communities so people know your expertise.
Think of audience tiers.
Rented Audience = Social Media or Digital Footprints
Owned Audience = Email lists in Newsletters
Monetized audience = Premium subs, selling products, services, etc.
Meaning: It is difficult to acquire subscribers initially if you don't have access to people. You end up publishing too much content without focusing on growth channels.
2. Money
Running ads, Beehiiv boosts, influencer marketing; things like that.
Slow organic growth builds authority but capturing subscribers early and fast in your journey gives you the scope to make early mistakes and iterate improvements fast.
From my experience - Content is not really the problem. Most creators/brands decently understand their audience and what content appeals to them.
They fail at setting up constant growth and monetization channels.