Ask HN: When to, when not to monetize?

Thinking of monetization on the paper stage of an idea distracts me, frequently. Many times it displaces the initial desired outcome.

i) How to quickly qualify an idea? Any Tips / Quick ways / Napkin methods / Indicators / Filters etc.

ii) How do you research after you have decided an idea can be monetized? If it is situational in your perspective, then some examples from the past (what you did) will be helpful. It is not necessary that you monetized that idea.