A lot of people think that a spiritual aspirant have to be perfect in every sense. The usual notion is that such aspirant can never lose their calm and confirm to an unshakable peaceful image. They are not expected to make any mistakes  and should be miles away from any kind of sin. While the above is desirable, in Bhagvad Gita, Sri Krishna admits that this is very difficult and every once in a while even the most diligent monks can make mistakes:

यततो ह्यपि कौन्तेय पुरुषस्य विपश्चित: |

इन्द्रियाणि प्रमाथीनि हरन्ति प्रसभं मन: || BG 2.60||

yatato hyapi kaunteya puruṣhasya vipaśhchitaḥ

indriyāṇi pramāthīni haranti prasabhaṁ manaḥ

 

The senses are so strong and turbulent, O son of Kunti (Arjuna), that they can forcibly carry away the mind even of a person endowed with discrimination and practicing self-control.

Sri Krishna further explains why this happens. According to him, every human is endowed with 3 kinds of characteristics, a) Goodness b) selfishness and c) ignorance. Every human is a mix of these three. In some people, goodness is more prominent but they can have little bit of selfishness and ignorance too. Similarly others might have prominence  of selfishness or ignorance with hint of the remaining two. Sri Krishna states:

रजस्तमश्चाभिभूय सत्वं भवति भारत |

रज: सत्वं तमश्चैव तम: सत्वं रजस्तथा ||BG 14.10||

rajas tamaśh chābhibhūya sattvaṁ bhavati bhārata

rajaḥ sattvaṁ tamaśh chaiva tamaḥ sattvaṁ rajas tathā

Sometimes goodness (sattva) prevails over passionate selfishness (rajas) and ignorance (tamas), O son of Bharat. Sometimes selfish passion dominates goodness and ignorance, and at other times ignorance overcomes goodness and selfish passion.

Whenever selfishness or egoism and ignorance becomes dominant character, the person is bound to make mistakes and hurt others. Does that mean that if such a person commits a mistake due these bouts, he commits a unpardonable sin? The answer is no.

While law of Karma will take care of the sin committed (sooner or later), it’s important for such a person to realize what has happened and keep his calm whenever the effect of Karma operates. They should consciously bring their mind back to righteousness from both selfishness and ignorance to perform unattached action

Sri Krishna states:

अपि चेत्सुदुराचारो भजते मामनन्यभाक् |

साधुरेव स मन्तव्य: सम्यग्व्यवसितो हि स: || 9.30||

api chet su-durāchāro bhajate mām ananya-bhāk

sādhur eva sa mantavyaḥ samyag vyavasito hi saḥ

Even the vilest sinners, who serve this universe (worship me) with exclusive devotion, they are to be considered righteous, for they have made the proper resolve.

Gandhi said hate the sin and not the sinner because every person in this world has goodness in him. It can be said that to bring this goodness out is greatest service to the mankind.

Om Shanti!