To how many things has anyone said "I would NEVER do that."
But somewhere down the line, whether tomorrow , next week, next year, or when ever.
But when the. shall we say, the "temptation" arises - You do it.
All it needs is the opportunity and to some extent the circumstances, to arise.
Of course if we are talking about being unfaithful to a partner.
The other factor to take into account is the "persuasivness" of the "other" person you may meet.
I can say "I will NEVER go sky diving." because its something that will not come to me and tempt me.
But if I meet a woman who looks, speaks, acts in a way , towards me, that arouses me. Then we are talking about something different.
To say "I would NEVER..." is being naive. Once the reason, motive, opportunity present themselves .... who knows.