People of the same thought and point of view are drawn to each other with a tendency to form an exclusive circle. A minority is apt to fence itself off from the majority, from the crowd. So it has been with the mystics. Mystical ideas are un-intelligible to the many. The mystics have therefore usually imparted their ideas to a chosen few only, to a picked band whom they could trust and who were ready for initiation and discipleship. Thus, great Sufis have appeared at different times, and founded schools of thought. Their expression of wisdom has differed to suit their environments; but their understanding of life has been one and the same. The same herb planted in various atmospheric conditions, will vary in form accordingly, but retain its characteristics.
from
https://wahiduddin.net/mv2/archives/sufism.htm