B requires A. C requires both A and B. But also, A has a cost and B has a cost, and spending more on A or B can maybe get you more C.
Maybe spending more on developing better computers won't actually help anything (because they've already got 640k memory, which is enough for anyone). But only half of the people who can benefit from them have actually bought one so far, so collectively spending twice as much on buying computers can make them collectively twice as beneficial.
B requires A. C requires both A and B. But also, A has a cost and B has a cost, and spending more on A or B can maybe get you more C.
Maybe spending more on developing better computers won't actually help anything (because they've already got 640k memory, which is enough for anyone). But only half of the people who can benefit from them have actually bought one so far, so collectively spending twice as much on buying computers can make them collectively twice as beneficial.