As shown below, at first I constrain two poles of "Purple" to the ends of "BLUE_1". When I try to drag the third pole to the end of "BLUE_2", it's impossible to be done! It seems that I need to set Movement to X/Y/Z and drag the pole to the target point for 3 times and finally get them coincident.
I never had this trouble before. Do I miss something important for Studio Spline?
ADD: I just find the solution --- set Movement to View.
Always fully expand your dialogs such that you're seeing everything - there may be important settings that you may wish to turn off and on under Settings (I believe that's where Associativity is controlled). If you don't turn on Associativity and move the parents to the Studio Spline, it won't update like you may expect.
Remember, you want single segment splines if at all possible if you're going the high quality surface route - tick that box as well.
You don't necessarily have to position all the poles in their exact locations the first time around. I often start out with a 1 degree single segment, drop the start and end (will be a straight curve), then up the degree and the poles between will fill in themselves. Next, I may click and drag the endpoints until I see the continuity buttons popup in the graphics window, where I can then set the continuity. However, I may choose to drag the interior poles first to get them in a reasonable location, then do the endpoints and continuity - once the continuity is set, you can only do so much with the adjacent interior poles - that will control the curvature or tangent magnitude (how sharp or flat a curved area might be). That's just me and I'm not going to say what I do should work for anyone else. Maybe one of the other experienced surface modelers will chime in with their preferred methods.
You can also turn on the curvature comb display to help guide the spline shaping process as you're creating the spline.
There aren't explicit instructions on how to make the right curves - that's one thing that can make this process so difficult to learn. It mostly depends upon the parent geometry with which you're working.