One line is called “wholeness.” The general public follows the one line, meaning one way. That is, each one has a part in Torah and Mitzvot [commandments], and each one assumes how much labor he must do in order to feel that he has done his duty.
Each one calculates if he has done as he thinks, and then he is satisfied and feels that he is walking on the path of the Creator, and each day he is advancing.
This is not so on the right line: He should do everything the same as those who walk on one line, but the difference is that those who belong to one line do not have any more deficiencies, while those who walk on the right line have difficulties because the left line cancels the right line.
The left line evokes the craving for spirituality, which makes him think that we must walk on the path of Lishma [for Her sake], that this is the main thing. Thus, it is hard for him to walk in Lo Lishma [not for Her sake], meaning he does not have the satisfaction that makes it worthwhile to go, since the left line evokes the craving and the lack for spirituality.
Conversely, the one line does not evoke any lack within him. Rather, he adds each time because he has what to look at, whereas the left line erases everything.