It was my grandmother's birthday, I couldn't not go.
'Nonno/nonna' — NON-na. Clear double 'n'. 'Compleanno' — com-ple-AN-no. Stress on the third syllable.
Use when explaining why you cancelled plans — retrospectively, after the fact. The double negative 'non potevo non andare' (I couldn't not go) is emphatic and very Italian.
The double negative 'non potevo non andare' is grammatically correct in Italian (unlike English which typically avoids double negatives). It means 'I couldn't possibly not go' — emphasising obligation. Grandmother's birthdays in Italy are sacred.
Era inevitabile, non potevo mancare.
It was inevitable, I couldn't miss it.
'Non potevo mancare' (I couldn't be absent) — strong expression of duty
Ero obbligato/a ad andare.
I was obliged to go.
Direct — states the obligation clearly without dramatising
Non me la sono sentita di mancare.
I didn't feel I could miss it.
Emotional rather than obligatory — expresses personal feeling of duty
The 'nonna' (grandmother) is a central figure in Italian family life. Her birthday, her Sunday lunch, her advice — all are treated with utmost respect. Missing her birthday for a social event would be unthinkable in most Italian families.