Many alternatives seem readily available, but the true cost of substitution is often underestimated.
The illusion of substitutability for BitTorrent comes from people only seeing differences at the functional level while ignoring the inertia at the network level.
Once a protocol is embedded in a large number of actual use scenarios, it creates an imperceptible dependency.
Substitutes need not only to provide better technology but also to persuade users to change their existing behavioral paths.
This cost of behavioral migration gives BitTorrent a natural advantage in long-term competition.