If you never stay long enough to finish what you started, it's hard to really accomplish anything. In my experience, that usually takes at least a year or two (usually two).
Also, if you run at the first sign of trouble, it's hard to really accomplish anything (or learn many things actually, since a lot of learning is failing and trying again). It's also expensive for the people managing you/teaching you and the org in general.
Those are the things people are concerned about when they talk about job hopping.
For anyone reading this - if you have a pattern of moving every 6 months, or a year - and it's consistent - there may be underlying issues (mental health, interpersonal problems, unrealistic expectations, lack of skills/fit to the role) that would be helpful to address. Long term, it is pointing to problems that are likely holding you back professionally, and may also make it more enjoyable being you if you worked on them.
That said - every time I've started a role or a job and said to myself 'this is terrible I should leave, but.... it's only been x time and I want to give it at least y amount of time' (where y was 6 months or a year), I've regretted it. The last time I had this happen, I knew I should leave literally 2 days in when my new manager cut short my supposed 3-6 months ramp up time to throw me directly into a particularly hard external customer negotiation issue.
I ended up burning out and damaging my reputation doing so trying to 'give it a try' - a year and a half later.
It's a balance. Look for patterns.