In Jain Dharma, Ashtami and Chaturdashi are considered auspicious because they are often used for tapas, fasting, pratikraman, and inner purification.

Why these tithis are valued:

• They are seen as good days for self-restraint and spiritual discipline.
• Many Jains observe upvaas, ayambil, sāmāyik, or poshadha on these days.
• The purpose is not that the date itself gives merit, but that it helps remind the soul to turn inward and reduce karma through ahiṃsā, संयम, and tapas.
• In the Jain tradition, such days are made spiritually important through devotion, repentance, and purification.

So, Ashtami and Chaturdashi are considered auspicious because they support Jain spiritual practice, especially fasting and आत्मशुद्धि.