You don't. Not with 100% certainty. Not 100% of the time.
Some days I feel so aligned on my path, everything seems to flow.
On other days, I can't shake off the feeling that I am full of BS ! Always have been. No sign of that aligned, flow-y feeling then.
How do I know which one is the real deal ? I used to imagine once you're on the right path, you just know it because it all feels right. It all aligns. All the time.
Now I have accepted that feeling of knowing is an illusion, fleeting at best.
The only way then is to show up and do what you have to do. Regardless.
I don't think we ever arrive. At least not any more than we already have. Wherever you go, there you are. Figuring it out as we go along, without knowing if we ever will, is the journey of life. I guess. I'm not sure. Not 100%.