Let me rephrase the question such that evasions via Tu quoque are rendered impossible: is there a known case (as in, a person) where Stoicism does work consistently? And if there is no such case (as in, no such person) where Stoicism works consistently - what is its measure of success?
First: What do you mean when you talk about Stoicism working - What do you think is the goal of Stoicism?
Second: This criticism is applicable to just about anything; does capitalism not "work" since just about any implementation has aspects that can be considered flawed?
You cannot generalize about an idea from people's failures to be consistent with their professed belief in it (other than perhaps that it appears to be difficult to act according to it in a consistent manner).
In the case of Seneca, it is also difficult to say whether he attempted to apply Stoicism 100%, how good his attempts were ("objectively"), or whether it is even possible at all.
> First: What do you mean when you talk about Stoicism working - What do you think is the goal of Stoicism?
As the goal of Stoicism is maintaining happiness -- and I'm referring to living in peace and harmony 24x7 -- via virtue, then it is said to "work" if it can achieve the said goal 24x7.
> Second: This criticism is applicable to just about anything; does capitalism not "work" since just about any implementation has aspects that can be considered flawed?
Irrelevant. One is a complex social phenomena; the other is pertaining to human psychology with specific goals. I could as well pick an example from the other end of the spectrum (of simplicity): eating less, for instance, leads to weight loss (or maintaining weight) - and this can be consistently demonstrated ... hence eating less "works".
> You cannot generalize about an idea from people's failures to be consistent with their professed belief in it (other than perhaps that it appears to be difficult to act according to it in a consistent manner).
I wasn't generalizing anything, and an idea/ belief is not necessarily a fact. The idea/ belief of the stoics is that virtue is sufficient for happiness. There is no doubt, in the mind of stoics, that virtue always leads to happiness (no exceptions). And it of course "appears to be difficult" - because virtue, being a higher-level cognitive function based on morality ("thou shalt remain calm" for instance), cannot consistently override the core emotions (wherein lies sorrow and malice), as humans all throughout the centuries have demonstrated time and again.
> In the case of Seneca, it is also difficult to say whether he attempted to apply Stoicism 100%, how good his attempts were ("objectively"), or whether it is even possible at all.
I doubt it is even possible at all (see above paragraph). Hence my "if it doesn't work, what is its measure of success?" question. If success that one is striving towards is ill-defined, one is probably fooling oneself.
Shouldn't the offended stoics (who down-voted my above comment asking a reasonable question) be practicing their own philosophy by remaining stoic (neither up-voting nor down-voting)? tongue-in-cheek.
[0]: https://en.wikipedia.org/wiki/Tu_quoque