Department stores use coffee beans to try to keep you from leaving the story. That's not totally diabolical in itself...that the stores are trying to do is get you to take your time and let the scent develop before you decide if you like it.
You see, it can take perfume easily 20-30 minutes to fully develop. It's reacting to your body chemistry, the humidity of the air, other molecules already in your nose, etc. As a matter of fact, you can sometimes smell a perfume more accurately by just walking outside...surrounding it with a new background.
Spray the scent, smell, don't decide...just notice. Do something else...smell your wrist again a few minutes later. Just notice what you feel...what images do you have, if any.
Most likely, the scent will seem to fade. It's because your nose still full of those molecules...your scent receptors are still bound. This will fade.
At some point, the fragrance stops shifting. It seems like it's blending with your body chemistry to create a new scent altogether. Your scent transformation has concluded...you are different.