>>16752652Basically, the Destiny Knot chooses 5 IVs out of the total 12 from the parents.
To start with, it picks which 5IVs it's going to use. You have 6 options:
x/A/D/Sa/Sd/S
H/x/D/Sa/Sd/S
H/A/x/Sa/Sd/S
H/A/D/x/Sd/S
H/A/D/Sa/x/S
H/A/D/Sa/Sd/x
You want H/x/D/Sa/Sd/S, so you have a 1/6 chance that it picks that spread.
After that point, it picks which IV it will use from which parent. If only one parent has the desirable IV, it has a 50% chance of choosing correctly. So, you get 5 1/2 chances. If both parents have the IV you want, then it's guaranteed to pick correctly, eliminating one of those chances of failure. The more IVs both parents have, the better your odds are.