[manquer]

Goodwill is realized only a sale yes. It is the difference between the fair market value of the assets and the price (i.e. value) paid of the asset.

FMV is calculated and updated in books periodically, price or value is only possible to account for if there is a sale otherwise any metric for value is not sound accounting wise, but that doesn't mean those things don't have value at all(or only on sale), they are just not accounted until then. It is for a good reason you wouldn't want a company to say use goodwill as a security for leverage for example. Goodwill does conventionally include intangible value like brand, some forms of IP, and things like customer(employee?) loyalty and so on.