I am always hearing two arguments when it comes to an individual's past behavior, one being, it's the past... leave it there and the other being that history repeats itself.
I do not think either idea is correct. It is true that you can not change the past. What's done is done and you can only move forward, but, how can you move forward without learning from the past? If we simply throw our hands in the air and say "Oh well, it's said and done now", without taking the time to learn from it, we will remain stagnant. The same is true for wallowing in the past, of course.
If we remember our past and take things from our experiences it is unlikely that history will repeat itself. We can know what went wrong, how it did and what to do in the future. If we just ignore our own personal histories under the guise of not being able to change it, we may very well end up making very similar mistakes.
So, that is about our own personal pasts... What about the pasts of others around us?
I do not believe in constantly harping on another person's past, especially if it was from a time period when you didn't know one another.However, a person's behavior in the recent past can shed some light on how the may behave now. Throwing ones hands up and saying "Well, it was six months ago" can lead you into having your own internal battle and of course, it may not. The thing is, I believe it is best to err on the side of caution.
I am not hypocritical. I expect people to err on the side of caution when it comes to me also. It wasn't all that long ago that I made some very poor choices and exhibited abhorrent behavior. It would be prudent to realize there is the possibility I could do the same thing again. I know in my heart I would never do such things again, however, only I know my heart. No one else can see into my heart, mind or soul and should realize that.
A persons previous choices and poor behavior is similar to the ideas about substance abuse and addiction. When you are a recovering addict or know a recovering addict, you realize an addict may always have a propensity toward addiction. An addict may never relapse, or the may relapse multiple times, sometimes they never truly recover. It would be foolish to assume they will remain clean for the rest of their lives and on the flip side it is silly to assume they will not be able to remain clean. You have to take things a bit at a time with a degree of caution as you keep your eyes peeled for signs. This train of thought will come in handy when you meet a person who has a past filled with the same behavior repeating. One shouldn't condemn them to never changing, but you also need to remember old habits die hard sometimes. A person also has to remember that old habits are easy to fall back into within themselves, also. No one is above any type of flaw.
We can only do our best to make the best choices for ourselves and learn from our pasts. We also can not expect others to blindly believe we are suddenly a changed person.