Risa

It's my head-canon conspiracy theory that the true workings of the transporter are hidden/obfuscated, even from the technicians and engineers, to avoid the existential dread of facing the truth: you die, and then it clones you.

All these systems to make it appear as if it's a single, consistent matter stream, to leave room for the possibility of a consistent consciousness or even soul. It all falls apart in light of William Riker. You can't duplicate matter. The only feasible explanation is that they got his scan, and successfully materialized him, but the signal that would have disintegrated the original failed.

Tuvix died because people couldn't accept how many times they had technically killed their colleagues, or commited suicide.