Exactly. It's very hard to do, we are pretty much wired to worry...there are many evolutionary benefits for excessive worrying. Stoicism just tries to direct that energy to the things you can control.

I am now dealing with two sick elderly parents. There are many many moments where I feel like dispair, fatigue, guilt or any other negative feeling. When these bad feelings pop up I actively try to focus on any task that can help their situation - make a phone call to some doctor or care provider, call them and ask them how they are, read about latest treatments etc. If I find that at this particular moment there's nothing much I can do - I try to let it slide. It's not under my control so no point in worrying.

It works surprisingly well many times, but there is no complete cure to worrying. Worrying is human.