GTM ClubSourcing is where most outbound is won or lost, and where the least attention goes. It is the work of translating "Series A SaaS with a new sales leader" into filters, signals and searches that produce three hundred accounts, then finding the two right people at each one.
The best sourcers are curious about companies and sceptical of data. They spot-check every list by hand, because a filter that looks right and a list that is right are different things.