Thinking we can add anything to Christ's suffereings is all ego. Realizing that Christ suffered because we suffer is what provides our salvation, not some blood debt from an original act of disobedience that didn't really happen. Picking our crosses has to do with building the Church (remember Jesus as carpenter), although in the days of the early Church, that often meant martyrdom, a witness to Jesus, not to mortification. Let the Shia do that.