Hazrat Moulana Ashraf Ali Thaanwi (rahimahullah) once mentioned the following:
This path of tasawwuf (self-rectification and reformation) is extremely sensitive and intricate. (One is in need of remaining in the company of a Sheikh-e-Kaamil who is well acquainted with this department of deen.) Through remaining with a Sheikh-e-Kaamil, if one is blessed by Allah Ta‘ala with the understanding of this path, then indeed, one will be fortunate and gain some understanding.
However, if one tries to acquire knowledge of this department of deen through merely referring to the books written in this field, then one will not gain a complete understanding of this path, nor will one progress in this path.
The person who tries to acquire the knowledge of this path through self-study can be compared to a person who merely refers to the books of medicine in health issues without studying under an expert doctor and remaining in his company for a considerable period of time. Such a person will not be able to run a clinic administering treatment to patients, and if such a person places his hand on the pulse of any patient (emulating a physician), it will not result in any good for the patient he is trying to treat (as he does not have any qualification and expertise in this field).
In the same way, the person suffering from spiritual maladies will not see benefit (through him referring to such a person who has no knowledge of the path for his self-reformation). If the patients follows the guidance of such an unqualified guide who has not reached completion in the field of tasawwuf, then who knows what incorrect treatments he will adopt, and instead of acquiring benefit, the patient will fall into problems and difficulties.
In order for one to know whether a person is a Sheikh-e-Kaamil and has acquired perfection in this field, he should see whether the Mashaayikh of the time (the senior, accepted buzurgs of the time) have attested to his qualification and expertise in this field.
Nowadays, there are many ignorant people who are regarded as Mashaayikh (but in reality, are not Mashaayikh), and through them spreading ignorance among people, they give a bad name to the path of Tasawwuf. May Allah Ta‘ala bless us with the correct understanding.
(Malfoozaat Hakeemul Ummat 1/150)