When we remember that we were having a thought in a determinate past time, there are available two interpretations.
The most common interpretation is to say that your thought was surely influenced by the age you had that time or by the past circumstances. In this case, if the thought was shameful or silly, you can easily find an excuse. If it was successful, you may claim your possession over it as if the thought would be a sort of a material thing, since it is conceived in its temporal limits as like as the other things are perceived in spatial boundaries.
Another interpretation is the understanding of the past thought as one which gained from its definite time the status of being a part of your life. Meanwhile, the indefinite thoughts move across your mind and you cannot decide which of them has really modified your life. Surely, it is harder to find an excuse for the past parts of your life.
Though it is difficult to live with no excuse for your past thoughts, the second interpretation has the advantage of making you aware of your past life. Moreover, the past thoughts become useful means for modifying your present life, because they are not only your possessions, but also they possess your life.