The failure is because they abandon the Noble Eightfold Path and focus on meditation only. These people become greedy, thinking only about what they will gain from practising meditation.
Out of the eight factors on the Noble Eightfold Path, they ignore seven factors and only focus on the factor of meditation, or samadhi.
Then, sīla (precepts) and pañña (wisdom) cannot be achieved. By focusing only on meditation, (Wisdom) pañña which arises from Right View (sammā ditthi) cannot be achieved and samadhi eventually becomes false samadhi.
The right practice always follows the Eightfold Noble Path, day and night.
We must integrate Dhamma and our work as one, and integrate Dhamma and our life as one.