One time I was interacting with a stranger (so long ago, I dont remember who. Possibly just a store clerk). At the end of the interaction they looked me in the eye and said 'Have a great day'. It took me off guard, but made me feel really good in a way I couldnt put my finger on. I now say the same thing to everybody I meet in my day, in the hope I can bring somebody else that same feeling and genuinely make them have a good day.

Question, where do you live? In America, and especially on the Pacific Coast 'Have a great day' is a phatic expression [1]. It is a common parting phrase and has lost any special significance that it might have once had within a conversation.

[1] https://en.wikipedia.org/wiki/Phatic_expression