The initial R:R should be the easiest thing to work out before you put a trade on. You work out your stop & your desired profit target area, and then you calculate the R:R. If the R:R is not at least 1:1 (IMHO) then you don’t take the trade.
Now this is the hard part, letting trades pass because they don’t meet your R:R requirements, and this is where the psych comes in, allowing yourself to let a trade pass, which may become a winner and move onto the next one which meet your requirements. In the mean time your spewin because you missed a winning trade, so your determined the next one your not going to let pass, even if it doesn’t quite meet your R:R and so on & so on.
To me that is why when every talks about developing a system it is not just entry and exit (which to me is the least important part). It is all including money & risk management. Once you incorporate all the factors and you know you have positive expectancy, then you can trust your system.
The main question any trader who trades with a system needs to ask themselves is “Do I trust my system” if yes, they will trade even if they run into a few losing trades, if no, well the circle never stops.