Why do I need a Summary Mapping when I'm already providing an Issue Key Mapping?

Question

When I'm performing an Import from a CSV file, why do I need a Summary Mapping when I'm already providing an Issue Key Mapping?

The data I'm trying to map to the current issues does not have the Summary field so this is impossible to import the data.

Nic Brough -Adaptavist- · Answer

Ah, you don't need the summary if all the updates have a key so that it's clearly an update.

Tom Bridges1 · Answer

But why? I'm supplying the Issue Key, so the importer should know which issue to put the Comment Body against. It makes no sense to require the summary too. The Comments I'm trying to import and stored in a table that links via the Issue Key, so the Summary isn't available.

Nic Brough -Adaptavist- · Answer

No, that's not what I said.  Summary is mandatory, but it's not a key.