The gemarah (megillah 13b, sanhedrin 93a) states that tzadikim are compared to haddasim. We also know that of the four species the haddas is described as only having a pleasant fragrance but not a pleasant taste (as opposed to the esrog which has both). Why then are tzaddikim compared to this deficient plant and what lessons can be learned from their comparison to the myrtle?
Sefer Shaar Yosef Volume 2 Page 132 says that the word Hadas w/ the Kolel = 70, which is Ayin - since the Hadasim allude to the eyes and each leaf of the myrtle is shaped like an eye. This is the reason Tzadikim are compared to a Hadas since they protect their eyes from seeing things that are prohibited.