"You can pass your life in an equable flow of happiness, if you can go by the right way, and think and act in the right way."
The "think in the right way" takes just a little practice. The "act in the right way" is the hard part, and the whole thing falls apart, in exactly the way you've noticed, without both. I've yet to achieve both, personally, though simply having "think the right way", with a little moderating wisdom from age, isn't nothing.
I think a trap in general with systems like Stoicism, or Zen Buddhism, or similar, is believing that thinking or knowing is anything more than one maybe-necessary-but-certainly-not-sufficient step.
(frankly, I'm not even sure what "go by the right way" means, yet, and would have to return to the original Greek to figure out whether it's just a summation of the two following ideas, or something separate—however, as I'm still working on "acting", I'll leave that for another day)
[EDIT] For those reading this without having read Meditations, it's heavy on duty and obligation, which is deep in the "doing" side of the above dichotomy. The "think the right way" is largely about ignoring that which one cannot control, but the trouble is that anything in the immediate past becomes "beyond one's control", which is where the parent's slipped-deadlines and such become easy to brush off without the duty-and-obligation and act-the-right-way habits balancing it out. Can absofuckinglutely confirm that if you get very good at the "think the right way" side, and only that side, it gets dangerously easy to not be bothered by failure or inaction.