....snip disc^h^h^h^h argument over "pipe-first" or "fitting-only" solder
technique...

I'll side w/ Dave here, Doug...similar experience w/ training for
production work, same technique.

The amount of heating required to heat the pipe to solder-melt point
isn't enough to expand the pipe to the point of constricting the gap
between it and the pipe and it's much easier to ensure both are hot
enough more quickly by adding hit to the pipe initially rather than
relying solely on the (relatively) poor conduction across that same gap
between the two not fully contacting surfaces...