In markets governed by network effects, a product's value to each user rises with the total number of users. Such markets often tip: once one platform pulls meaningfully ahead, its growing value advantage attracts still more users, and laggards are starved of the very base that would make them attractive. This dynamic alters the logic of pricing. A firm may rationally set its price below cost early on, forgoing immediate profit, to accumulate users faster than rivals and reach the 'critical mass' beyond which adoption becomes self-sustaining. The wager is that once the network tips in its favor, the firm can later raise prices and recoup the early losses, because switching away would cost users access to the large network they now depend on. The strategy is not without hazard. If several well-capitalized firms pursue it at once, each subsidizing users to outrun the others, the contest can dissipate in losses no single firm recovers, for the market tips only once and toward only one. Penetration pricing thus rewards not merely aggression but the judgment of when a market is genuinely prone to tipping and when the prize is worth the subsidy required to claim it.