There isn't one thing but a combination of many factors, all of which I have covered off as best I can with my IC's.
If this is the case, then there is a better way to answer the question. I can't tell you how to state it, because that has to come from within yourself.
For me, it might be something like this:
I've learned that for a multitude of reasons, I don't have a very high opinion of myself. I have relied on others to pick me up through compliments and other forms of external validation. In any long term relationship, like a marriage, that's not sustainable. There will be times when your spouses opinion of you will not be a good one because you did something that bothered or hurt them. In those moments in my past, I turned to others to keep me from hitting bottom.
Knowing that now, I've used resources like counseling and The Assertiveness Workbook to find ways to build my own self talk track. When we hit a low point as a couple, I leverage those new skills to pick myself up rather than asking others to boost my feelings. Since I don't need to rely on the adoration of others, there's no reason for me to look anywhere but to my BW and family who love me for support. That's what will keep me from making the same choices in the future as I did in my past.
When you can give an answer that outwardly shows you know what traits caused you to choose to stray, and what skills or techniques you are using that ensure you won't do it again, it becomes a step toward the assurance your BS needs. Don't get me wrong. 100% blind trust is highly unlikely to ever exist again. But you can reach a much safer feeling as a couple when you can state clearly what ensures you won't inflict that same pain again.
[This message edited by Listeningclosely at 1:51 PM, August 15th (Friday)]