In Jain Dharma, we don’t observe every tithi with special rules because:

1. Some tithis are especially powerful (adhik punya)

Our acharyas have pointed out certain tithis where the fruits of tapa (fasting), jaap, paath, pratikraman, etc. are much greater than on normal days. - Examples: Aatham, Chaudash, Poonam, Amavasya, Chauth, Do Tithi, 5‑tithi, 16‑upvaas, etc. ( jainknowledge.com) So most people take niyam (regular vows) on these few days instead of all 30 days.

1. Practicality for grihasth (householders)

- Full‑time tapascharya every single day is the ideal, but very hard for one who has family, business, work, etc. - So, Shastras and acharyas have given niyamit vrata – “I will surely do special dharma on at least these tithis every month.” This keeps discipline lifelong, without making it impossible.

1. Focus and regularity

- When we know “On Aatham–Chaudash / 5‑tithi / Do‑tithi I have niyam”, we prepare mentally and physically. - It becomes easier to maintain purity in food, control over senses, and time for pratikraman and swadhyaya on those fixed days. ( jainknowledge.com)

1. Connection to Jain history and events

Many special tithis are linked with important events of Tirthankars and great saints (janm, keval‑gyan, nirvan, etc.). On such days, doing tapa and upvas is considered very beneficial. ( jainknowledge.com)

1. Every day is for dharma – tithis are “bonus days”

- Basic Jain rules (ahimsa, satya, aparigraha, avoiding root vegetables, not eating at night, etc.) are for all days. ( jainknowledge.com) - Special tithis are like “bonus” days where we do extra effort: upvas, ekasana, ayambil, more prarthana, more swadhyaya.

So we observe only a few tithis every month in a special way because:

• They give extra punya,
• Are practical to keep regularly for a whole life,
• And are traditionally selected by acharyas for higher spiritual benefit.

If you tell me which niyam you follow (e.g., Aatham‑Chaudash, 5‑tithi, Do‑tithi, 16‑upvas), I can briefly explain that specific vrat also.