but you can take a simple action to prevent it at a low risk or little cost to yourself.
Here is where you argument came off the rails.
It is not low-risk. Nor is the cost little.
How can you stop the lady pictured above from walking off of a cliff? Every way that would be called "easy" can, and has, landed people in jail.
All she has to do is claim rape, or assault, or crazy psycho stalker.
All she has to do is claim that she wanted to see the beautiful view.
And once you are arrested (have your future job prospects destroyed) she can leap to her death in peace.
Next, is how can you tell if what you are doing will help someone. By trying to save someone from walking into a precarious position, you may put them in a worse position.
If we are indeed talking about suicide, then that is even a worse case. Where you will need to put in considerable time to talk the person into believing their is a future. And not once, but three times. It is incredibly difficult work. And will usually leave you feeling tattered, if not outright depressed (and that is if you do not fail)
Trying to save someone is often very difficult and fraught with much peril. (just ask a life guard) However, it is, to me far better than living with knowing you could have helped.