(if you wish to submit a question for this series, please write to massimo at howtobeastoic dot org)
B. writes: I would like to ask what do you think Stoicism has to say on the topic of ruminations over unhappy memories. I, as probably a lot of people, tend to randomly remember such, and sometimes it takes me minutes to calm down. I know all the reasonable answers like: you were a child, you couldn't know better; no one remembers it except you; even if, it doesn't matter; we all have learned our lessons since that time. But sometimes it feels too little. What would be the Stoic advice in such cases?
Very good question. Of course, all the reasons you list for not dwelling on unhappy memories are indeed valid. The Stoic take about this, however, is even more straightforward. Even if, say, you should have known better, or if other people do remember it, or if it did matter, the fact is, the past is no longer up to you, and dwelling on it violates the dichotomy of control, and it represents a misapplicaton of the virtue of practical wisdom (the one that tells you that the only truly bad things for you are your current bad judgments). Here is Seneca on the matter:
Souls that enjoy being sick and that seize upon excuses for sorrow are saddened by events long past and effaced from the records. Past and future are both absent; we feel neither of them. But there can be no pain except as the result of what you feel. (Letters to Lucilius, LXXIV.34)
What benefit is there in reviewing past sufferings, and in being unhappy, just because once you were unhappy? (Letters LXXVIII.14)
Two elements must therefore be rooted out once for all – the fear of future suffering, and the recollection of past suffering; since the latter no longer concerns me, and the former concerns me not yet. (Letters LXXVIII.14)
That said, Seneca himself also advices to learn from our mistakes:
I shall keep watching myself continually, and – a most useful habit – shall review each day. For this is what makes us wicked: that no one of us looks back over his own life. Our thoughts are devoted only to what we are about to do. And yet our plans for the future always depend on the past. (Letters LXXXIII.2)
This last piece of counsel is not at all contradictory with the sentiment expressed in the first three quotes. It amounts to the difference between detached analysis of our past mistakes (a good thig) and regret, the emotional clinging to mistakes that is not in our power to change (a bad thing).
Now, this is the theory. But as you say, sometimes thoughts just stubbornly intrude into our consciousness, they are hard to let go, and it takes us time to recover from their intrusion. There is a way to deal with this in the Stoic spirit, and it has been updated within the context of cognitive behavioral therapy.
Every unhelpful mental attitude we have -- not just the specific one we are talking about -- can be addressed by: (i) Taking the cognitive step of analyzing the attitude and telling ourselves that it is irrational, or not helpful. We can do this by way of literally talking to ourselves aloud, or by way of talking to a friend or therapist, or by writing our thoughts down. (ii) Implementing practical strategies to redirect our behaviors. And (iii) Repeat steps (i) and (ii) until our mind habituates itself to let go of the bad habit we are trying to correct.
Step (ii) can be implemented in a variety of ways, in the case of intruding thoughts. One of my favorite (which is not found in Stoic writings, but is imported from Buddhist meditation) is to close your eyes and imagine that you gently pick up the troubling thought, put it on a leaf, put the leaf on a running stream, and watch the thought drift away. Alternatively, I mentally visualize swiping -- again, gently -- the thought away from my mind, replacing it with something positive or pleasant as an alternative.
I have implemented these strategies for some time now, and I have noticed a marked decrease in the frequency of the sort of mental intrusions you are bothered by. Of course, remember that what I wrote above is a combination of philosophy and psychology, not a magic bullet. The problem won't go away, and certainly not overnight. But improvement is certainly at hand. Then again, only the perfectly wise person will never have regrets, and sages are as rare as the phoenix.