It is a tempting instinct, especially for anyone who has struggled to find a scent strong enough to last: if one fragrance is good, surely two or three at once would be even better, more coverage, more staying power, more of a good thing. In practice, this almost always backfires.
Fragrance does not stack cleanly the way most people assume. Two distinct, well-built scents diffusing into the same enclosed space at the same time do not simply add together into a stronger version of both. They blend, usually into something muddier than either scent alone, since the individual notes that made each fragrance distinct start competing rather than combining.
There is also a practical cost to doubling up that people rarely account for. Running two or three cards simultaneously means burning through all of them at once instead of one at a time, which shortens how long you are actually stocked up before needing to restock, all in exchange for a result that usually smells worse than a single well-chosen scent on its own.
The better instinct, if you want variety, is rotation rather than layering. Run ONE for a few weeks, switch to FOUR for the next stretch, rather than hanging both at once and hoping for the best. This gets you genuine variety over time without ever muddying a single drive, and it means each card gets to do its job cleanly instead of fighting for space with something else.
If a single scent feels like it is not doing enough, the fix is usually a better fragrance, not a second one stacked on top of it.