I have been travelling a lot more recently and trying to wrap my head around how one gets upgraded to business/first class from couch. It seems to be inconsistent and i dont get how it works. For example, I always fly first class domestically and many times I will be sitting next to an empty seat, and right before take off, someone from couch is upgraded and sits next to me. I find this a little annoying, as I know i paid a lot more money than they did for the ticket. However, there is a HUGE difference between the price of couch and first class for international travel. So that brings me to my main question.

I am looking at flights to Japan in a few weeks. Couch is 1000-1500 for round trip and first class in around 5-6000. I am going to find it extremely annoying if I pay the 6k for first class and then someone who paid 1k for couch gets upgraded to the pod next to me. I have heard conflicting stories about international travel and that some airlines will upgrade you from couch to first class and some simply will let the seat be empty because of the unfairness of someone paying 5-6k for 1st and then having a passenger pay 1k and then get upgraded.

I am just trying to figure out my play, If 1st class seems to be empty before the flight, and upgrades are available (i dont even know how one goes about getting upgraded), then it seems to make sense to roll the dice, get economy comfort and see if I can get upgraded. If there is no chance to get upgraded on International flights then that makes the decision easier - either take some xanax and do economy comfort or just pay the high first class fees.

Any frequent travelers help me out?