privatereason

2. A reason known only to a small group and not shared publicly.

The board's decision rested on a private reason kept from the press.

3. A personal belief or logic that guides someone's choice without being announced.

He chose the smaller house for a private reason: it reminded him of home.

4. An internal justification used in one's own thinking rather than in public debate.

Her private reason for studying late was simply that she loved the subject.