Right off the Back

A phrase referring to a specific personal, social, or worldly event that an individual has experienced or observed in the past, and shares their memory of while in a conversation, or while reflecting on the significance that he/she knew at the time would create a long term and/or an unavoidable chain of events.
This term implies a strong sense of intuition from the observer, as well as some experienced time that has proven the significance of this event to be be truly valid.
(*Not to be confused with "Right off the bat", which typically refers to a quick and strong , but short lived response to an emotion or action.)

The first time I walked through her door, I knew right off the back that she would be the love of my life.

When I first read in the newspaper in 1991 that it the US invaded Iraq to defend Quwait, I knew off the back that it would start a chain of events that would pull the U.S. into a long term military engagement in the Middle East.