You smell something on a friend, buy it, and it is not the same fragrance. This is not imagination and it is not a fault in the bottle. Skin is part of the composition, and no two people supply the same one.
Skin is a solvent, not a surface
A fragrance does not sit on top of skin. It dissolves into the film of oil there, and that film differs from person to person in quantity and in composition. More sebum means more of the heavy molecules held and slowly released; less means a faster, thinner wearing. This alone can separate two people's experience of the same bottle by hours.
Skin surface pH varies between people as well, and mildly acidic skin treats some materials differently from skin closer to neutral. The effect is smaller than the internet generally claims, but it is real, and it falls hardest on the materials that are already unstable — certain citruses, some florals.
Heat, and what you ate
Warmer skin projects more and burns through the opening faster. Body temperature is not constant: it moves with exercise, with the weather, with the menstrual cycle, with alcohol. The same fragrance on the same person in Delhi in June and in January is not doing the same thing.
Diet contributes at the edges. Garlic, cumin, fenugreek and alcohol all leave the body partly through the skin, and what they leave becomes part of what anyone standing near you smells. So do medications. So does smoking, heavily.
Paper tells you what the perfumer made. Skin tells you what you will wear. They are not the same report.
Why the blotter lies
A paper blotter is chemically inert and holds nothing back. It shows the composition as constructed — every material in its intended proportion, developing in its intended order. That is exactly why it is the wrong test for a buying decision.
On paper there is no oil to dissolve into, no warmth to push the top notes along, no acidity, nothing to react with. A fragrance can be beautiful on a blotter and wrong on you, and it can be unremarkable on paper and become something else entirely an hour into being worn.
Use paper to decide whether a composition interests you at all. Never use it to decide whether to buy.
How to test properly
One fragrance at a time, on clean skin, with no scented moisturiser underneath. Two sprays, then leave it completely alone — no sniffing at the wrist every three minutes, which exhausts the nose and tells you nothing. Go and do something else.
Come back at hour one, at hour three, and at hour six. The last of those is the one that matters, and it is the one almost nobody performs, because it requires having the thing on your skin for most of a day rather than for ten minutes in a shop.
This is the entire reason a 2 ml vial exists here at ₹250, credited back against a full bottle, and why the discovery set carries all five. A decision made at hour six is a different decision from one made at minute two.