Direction of a merge
One profile is merged into another. It's not that the two profiles are combined into a new, third profile. Therefore, the "direction" of a merge matters.
We always merge a new duplicate into the original, first profile.
The only exception is when the original profile had an incorrect Last Name at Birth. For example, a duplicate of Benjamin Franklin, e.g. Franklin-2, would be merged into Franklin-1. But if the original was called Franklyn, it would be merged into the first profile named Franklin.
See:
Help:Merging
Help:Merging FAQ