This post is super-quickly written and mostly for reference.

Setup:

• precondition: agreeing with the idea. (here synonymous with holding a belief in the idea)
• beliefs are intertwined. When you update one belief, you often have to update other beliefs to maintain consistency.
• E.g. if you update to "my friend has Covid", you should also update to "I might have Covid"
• all these intertwinings form belief networks, where, if one belief is updated, the whole network might have to update accordingly

Taking an idea seriously means 2 things:

1. updating your whole belief network according to the idea, including when that updates you towards weird or "out there" belief states

• e.g., taking "animals can suffer" seriously, should update people towards "veganism good" (neglecting more complicated belief networks for a moment). However, many people find that too weird or radical intuitively and don't update properly; they fail to take the idea seriously

2. acting on your updated belief network

• e.g., because of the updated belief "veganism good", a person might reduce their consumption of animal products. Many people don't take this step and, while agreeing with “veganism good” intellectually, never reduce their consumption of animal products; they fail to take the idea seriously

Related:

Kuhan on Taking Ideas Seriously 

https://www.lesswrong.com/posts/N99KgncSXewWqkzMA/compartmentalization-in-epistemic-and-instrumental