This is a great question to discuss. I thought this would be very inherently obvious to me at this point, but it did make me wonder.
The clue to answering this is that the necessary condition in a given condition is the one that always occurs. (Rather than the sufficient). Dissecting it this way makes us realize that in any given sentence, "always" denotes necessary.
I am always happy when I eat ice cream
Ice cream -> Happy
The dog always plays
Dog -> plays
Etc.
I hope this helps. Please let me know if you have any other questions!