Hasan li-dhatihi meets the essential conditions within its own transmission: uprightness, adequate albeit lighter precision, continuity, and freedom from disqualifying defects. Hasan li-ghayrihi can arise when a weakness in a particular route is capable of being compensated by credible, sufficiently independent corroboration.
For example, a connected, defect-free chain through a reasonably precise narrator may itself be intrinsically hasan. A report from a mastur (a transmitter whose inner reliability is not established) might remain weak when isolated but become better supported if meaningful corroborating routes exist.
Caution: not every weakness can be repaired through more chains, and apparently multiple chains are not necessarily independent.