How can you ever know what is best for yourself?

You can never know what’s best for yourself because the world, and your place in it, is ever changing. What was best for you yesterday might be bad for you today and there’s no second-guessing tomorrow.

Your best bet it to strive to do what you believe is right and just as much of the time as possible. If your intentions are good, you can be forgiven almost any transgression and if you keep a positive outlook other like-minded people will gravitate to you and you’ll have each other’s backs.

Keep your self in prospective from yourself. Very few of us are in this alone, and even fewer are successfully ‘an army of one’. Build yourself a social safely net and then it becomes what’s good for the group is what’s best for yourself.

We can’t. How could we possibly? That’s an overwhelming amount of pressure to put each individual under. We have to make choices based on what we perceive in the moment to be best – not just for ourselves, but for everyone – and then we have to forgive ourselves for not getting it any better.

I do, but I can’t afford to have it anymore. lol
What’s best for me, lends itself to great joy, peace, happiness, contentment?
Being semi-retired, living on a beautiful rural property, traveling, exercising my abundant creativity, just BEING, and enjoying my one life.

Pffft..I had that lifestyle for the last 11 years until this economy wiped me out.
Now I am existing, survivng, but given the measuring stick I had, it’s a shitty life.

Have as many experiences as possible, and study philosophy. Nicomachean Ethics is a good place to start with your question because in this book Aristotle explores how to live well. He argues, in brief, that the highest aim is to happiness, and that cultivating reason in thought and speech is the work of living.

There is no way to be 100% certain! but I find the gauge of whether I will be able to sleep with a clean conscience and peace-of-mind, or would I have regrets about my decisions on my death-bed to be quite effective. Not all decisions can really be made that way, though. I recall having to decide between two job offers – one part time, closer to home, and consistent with what I enjoyed, the other full-time, further away, and less interesting. I chose the latter as a single mom, since I needed the money; but it was such a poor fit, I was miserable. Of course, I have no way of knowing whether the part-time position would have had me feeling better-fulfilled and have gone to full-time; so as I said, we can never be absolutely sure.

As @ibstubro, @glacial & @hearkat have noted, you can’t. Most of what we do, we don’t even think about. We normally don’t decide when to take the next breath. We certainly don’t decide when our heart will beat and when it won’t. And for those things we do think we consider, generally have many options and can only exercise one of them. We will never know what the outcome of any of the other choices would have been.

If it’s worrying you, read Sam Harris’ excellent little book, Free Will. You will find you probably don’t have any, and it won’t change a thing about how you live your life but it will free you up from agonizing about opportunities missed.