Word for the instance of something that makes you appreciate things like it

Question

I'm looking for a word which describes the instance of a thing that causes you to become interested in that thing more generally.

For example, perhaps you are a person who has never cared much for sandwiches, then you have a sandwich that you find particularly delicious. Now you love sandwiches. You live for them.

Example sentence:

"That was the NOUN/ADJECTIVE sandwich. Now I'm a connoisseur."

The best word that I can find is "gateway," as in a "gateway drug," or in this case a "gateway sandwich." But I think this meaning is only colloquial. I don't see gateway having this definition explicitly in any dictionary.

Answer 1

The best (compound) word that I can think of is "eye-opening" (adj.) or "eye-opener" (n.):

(of an event or situation) unexpectedly enlightening.

Source: https://en.oxforddictionaries.com/definition/us/eye-opening

It has its roots in the context of religious enlightenment ("My eyes were opened and I saw the light."), but it is very commonly used in non-religious contexts today.

Answer 2

Catalytic is the adjective comes to my mind, but a noun such as impetus does the job too.

Answer 3

I suggest:

from Oxford Living dictionaries online https://en.oxforddictionaries.com/definition/breakthrough

breakthrough

1A sudden, dramatic, and important discovery or development.

‘a major breakthrough in DNA research’

1.1 An instance of achieving success in a particular sphere or activity.

‘his big breakthrough came in 1988 when he had two paintings accepted by the RSA’

as modifier: ‘the band's breakthrough album’