I would add to what Jim and Better Living said, that right is when it looks right BUT it may take some refinement in your sense of what looks right - this takes some time and experience - The curvature graph is a very valuable tool in helping you see where to make adjustments cause it is not always immediately obvious from the pixels on the screen. So looking right usually ends up meaning nice progressive curves with visually logical transitions and accelerations etc.
My favorite dead simple example is the difference between Rhino’s old
Blend command and the newer
BlendCrv at its default settings. Both make perfectly good curves that are G2, to the lines in this case, but the graph helps show what is ‘wrong’ with the Blend result - it has two separate ramps up in curvature, and the curvature ‘flattens’ over the largest part of the curve. Depending on scale and material finish, this will show a somewhat abrupt reflection if it is made into a surface. The BlendCrv has one ramp up from either side to a single high curvature in the middle, more like a conic.
To me the latter has more logic, if that is the right word, and is usually what I shoot for. The Blend version is better if you are looking to more closely approximate a round fillet, only have it G2, on the other hand, and I suspect that was the intent when the command was made, eons ago.
BlendCrv on the left this time, Blend on the right.