I'm presuming that you are talking about this decision in the context of repeated failure of your core product/service when you still have (i) money left in the bank for at least another 6 months, (ii) a team that wants to continue to work together and (iii) supportive investors who are not clamoring for the rest of their money back. If not all three conditions hold, then you should probably quit.

Pivoting is the easiest of these decisions to make. You pivot when you see some element or subset of your product that is getting way more traction than what you thought was your core usecase.

Sometimes this is because users are focusing on one element of what you do, sometimes they are asking you for a set of features that are different from what you have in mind, sometimes they hack your product to use it for something you didn't expect, sometimes all the usage falls around a single usecase that is a "corner case" for you.

You want to see this from a lot of users, certainly the plurality, but when you do, you should pivot and gives users what they want, regardless of the product roadmap that you have in mind

Sticking should be the most difficult decision to make. I have assumed repeated failure of the core product, i.e. you're out of ideas, it isn't just another feature that is needed, you've hired who you need to to fill in gaps in your team, and it still isn't working.

If this is not the case and you feel like you might be one turn of the crank away from cracking the market, then crank on. But this requires real, intellectually honest discipline. It is easy to incrementalize "one more release". You should set success criteria for yourself (whether based on time or on new releases), and if you fail to hit those criteria, then you need to really assess whether or not you are still on the right track.

This doesn't need to happen only when you are out of money, it should ideally happen on a regular basis.

Quitting has a lot of negative connotations, and among answers to the question "What three words are the most useful and generally applicable pieces of advice for startups?" are variations of "never give up".

I think this can lead to bad outcomes. The most valuable resource for an entrepreneur is their time, and if they are wasting it on a quixotic startup, they will never get that time back. But when you're winning, when you're REALLY winning, it feels easy. If it feels hard all the time, then you are probably doing something wrong. And when you're doing something wrong all the time, then you should probably stop.