"...as even 1 patient is enough to destroy everything"

That implies we are trying to make the virus extinct, which we are not. We want the virus to spread, but at a manageable rate.

Right, my point is that a single lockdown is not enough. You have to have good monitoring and intermittent lockdowns in different areas based on that monitoring

Which would further imply that circumstances must change to get that manageable rate as long as group immunity is not proven and a vaccine is still lacking. The circumstances pre-lockdown allowed the virus to easily travel beyond China. Both measures and mindset in many Western countries are still incredibly lax. The symptoms mimicking those of cold, flu, etc. also don't help. People value their current freedom, privacy and hyper-mobility way too much for a manageable rate to come to fruition without locking down.

Otherwise you'll just end up with a new trend of locking down things for 2 months, then opening up, only for a new patient 0 to lock down everything 2 months later.

I don't think "we" have any desire so clearly defined and articulated as that. This virus so so extremely contagious and deadly that there isn't a manageable rate that is going to get us to a high fraction of immunity within the next two or three years. And the measures apparently required to keep it from growing explosively are pretty extreme. I think that China actually does intend to eradicate the virus domestically, and, tbh, short of a vaccine I'm not sure there's any other politically acceptable exit from this situation. Fwiw I don't think allowing millions of deaths is politically tenable, and I don't think that "lock down the only the vulnerable" is going to work.

(I wish I could believe that contact tracing and partial lockdown were sufficient but even Singapore, which by all reports was doing these things, is now SIP with 1/4 as many cases per capita as the US. I think our best case if we can't eradicate is going to look a bit like SK, where schools are shut down and life is very different from what we would typically expect. But that is a best case scenario assuming competent and diligent institutions, which I'm not sure we have.)