As the technical experiment that it was meant to be,  indeed bitcoin has not failed so far. Namely, the protocol designed by "Satoshi" has motivated enough volunteers to keep the blockchain updated and secure, non-stop, for almost 6 years now; and no fundamental security problems have been found.  (I gather that a bug made it necessary to rewind the blockchain some years ago, but it was not fundamental and quickly fixed.)

However, the experiment cannot yet be called a success, because it is not finished yet.  Mining is still supported by an "inflation tax" that increases the money supply to 5-10% per year.  At some point, that reward will be insufficient, and miners will have to depend on transaction fees.  In theory, the protocol should still work in that regime; but the point of the experiment is checking that the theory works in practice.  The experiment will be a success only if the network continues to function after that transition.

While the experiment has not failed so far, some developments, which may have been unexpected, suggested some potential problems that have not been adequately dismissed yet.  In particular, mining turned out to have substantial economies of scale, so that it has become concentrated in a handful of large companies and pools.  That increases the likelyhood of "51% attacks" and double spending in transactions with few confirmations.  It may also give the large mining companies the same oligopoly power that banks now have over international money transfers, with the same results.

Moreover, if there will be a large decline in price, difficulty will have to drop while some of the hashing equipment will have to be switched off.  Thus, at some point there may be enough idle hashing power in the hands of a single entity to mount a surprise 51% attack.

Also, its apparent anonimity (which was not a design goal, but merely an inevitable consequence of the "trustless" goal) attracted substantial criminal use.  It also made bitcoin theft and scams easy, profitable, and difficult to fight.  The huge price increase (partly driven by its illegal uses) caused all sorts of problems in itself.  It attracted people who were not interested in the technical experiment or its real goal, but only in the speculative potential.  A few people accumulated large hoards of cheap coins, reducing supply and leading to even higher prices (and unheard-of volatility).  Some investors have been trying to convince computer-naive people to buy bitcoin as a get-rich-quick scheme, or as a way to escape inflation.  As a result, bitcoin got a bad public image and hostility from many governments.  These developments do not yet threaten the technical experiment directly, but could do so if bitcoin gets banned over most of the world.


The jury is still out on that.  There have been many things "backed by nothing" that were highly prized and profitable -- for a while.