Back in the day, I sold scented candles. Each year, we would drive down to Phoenix for an annual convention. At one of them, they had a seminar featuring a psychologist and a perfumist. The psychologist explained how we form memories and that the "image" stored in our subconscious is a combination of all of our senses: sight, smell, sound, taste, touch, and emotion. Any one of the senses can evoke the memory, and thus the emotion. We may not even be aware of it, we just feel up or down.
The perfumist had formerly worked for a big cosmetics company. She explained how scents are created and had us do experiments by combining the scents of different candles, then notice if it triggers a memory, or if it is something that you just like or dislike.
I discovered a very interesting combination accidentally while unboxing candles at the State Fair. I opened a large Lily candle and a small Rose candle, and the combined scent was heavenly. I don't know why, but I love it.