Well, yes and no. Of course, we don't get 100% success results (would you know anything or anybody who does by any chance?). However, when it doesn't work, one could start exploring why exactly it doesn't.

Quite often, the person might be doing it on their own, after only one reading of the manual or one session with a practitioner. Then they might need a little bit more assistance or guidance in order to use EFT at its best to get the results they'd be looking for. And if they are experienced EFT-ers, they'll know that sometimes we just need someone else to show us the way out, and they'll request help from a fellow EFT-er or a practitioner.

If they are working with a practitioner already, maybe the exact issue is still to be uncovered? Maybe the person is not ready to accept healing or resolution (and even that could be "tapped on"!)? Maybe it needs someone with a little bit more expertise to find out the key and unlock the problem? Persistence sometimes opens unexpected doors.

EFT has now gathered thousands of highly improbable successes, from cancer to PTSD including MS or getting people out of wheelchairs. And that's excluding all these everyday worries and bruises that you might have already solved by yourselves. Coincidences? Scientific research is on the way to support these successes with scientific evidences. Meanwhile, you can decide for yourself.

You can never be sure that all avenues have been explored. If you ask a practitioner about their success rate, they'll probably state something between 80% and 99%. Never 100%. So yes, I guess you could say it doesn't always work. 

But if you don't put all the chances on your side to try it out, how will you know if it could work for you?