How should I enter a market that’s an established idea?

Overall, established ideas mean you'll be competing on price/features and may not have the opportunity to set the tone in the culture - i.e. be a leader. Nothing wrong with that - but usually when we see something like this, the question we need to ask is whether there's a subspace or a nuance within that overarching topic or area that in fact does offer innovation opportunity.

For example, gluten-free foods may not offer an innovation opportunity but gluten-free food made with whole foods/ingredients might (especially if it links to the high-fat, low-carb diet culture).

Our team can help you figure this out.

It is also important to note that cultures that are well into the established idea stage also tend to be prone to a full reset. For example, a brand new disruptive product or solution can from time to time completely reset well-established cultures and push them back into the early consensus stages. [Culture is after all, cyclical.]