At 2 influence, it's hard to find a spot for The Source in most decks. It requires the support that a (Criminal) connection deck provides.
Hostage is a tutor for The Source, so there is no need to waste influence and deck space for more than one copy. (notice Thomas Haas in both card arts)
Fall Guy prevents it from being trashed when an agenda is scored/stolen.
Dr. Lovegood can blank it during the Runner's turn. It's worth noting that this not only negates the 3 drawback, but also prevents it from being trashed when an agenda is stolen. This lets you save your Fall Guy for a rainy day, or use them for other cards.
But wait, what does The Source even do?
It essentially does two things; choke agendas in HQ, and/or give the Runner a window to steal if the Corp attempts to score. Detailed explanation below.
When the Corp installs a card in a server, it can be an asset, upgrade or agenda. If it is a 3/2 agenda, the Corp can score it in the following turn. It is often very inefficient (and unsustainable) for the Runner to run every card the Corp installs. The Source solves this problem.
With The Source on the board, 3/2 agendas become 4/2. Without the assistance of FA cards (Biotic Labor, SanSan City Grid), these agendas have to be installed and advanced once to score it the next turn. Which means the Runner will know that the installed card can be advanced. This narrows down the possibilities: an Agenda, an important Asset, or an Ambush. Either way, it makes the Corp think twice before laying down an Agenda.
Of course, this does not only apply to 3/2 agendas, but to ALL agendas. 5/3s takes a long three turns to score. 2/1s and 4/2s lose a lot of their tempo. Naturally, Criminals have the best cards to maintain and take advantage of this board state.
**This is my longest review yet, do leave a like if you enjoyed it. See you 'round the net. ;)