A perfume is a timeline, not a single smell. That is why the first sniff in the store can disagree with the scent on your sweater six hours later.
Top notes are what you smell first: citrus, light herbs, aldehydes, some fruits. They evaporate quickly. They are the handshake.
Heart notes (middle notes) show up after the opening fades: florals, spices, tea, many green notes. This is often the character of the perfume.
Base notes are the dry-down: woods, musk, vanilla, amber, resins, patchouli. They last the longest and are what people smell when they hug you at the end of the night.
A perfume that opens bright and dries down sweet is doing its job, not “changing on you” in a broken way. If you only like the first five minutes, you like the top notes. Shop the dry-down, not the cap.
When you read a note list, look at the base if you care about longevity. Vanilla, sandalwood, and musk tend to linger. Lemon and bergamot often do not.