What does the non-conclusive element in the definition of wajib signify?

Prescribed Acts and Prohibitions: Fard, Wajib, Sunnah, Nafl, Haram, Makruh, Azimah and Rukhsah

• Performance and omission become equally permissible
• Evidence remains authoritative but not decisive, while performance is still binding
• The proof is nothing but baseless opinion
• Wajib is assigned by personal taste alone