You're supposed to score. I believe the method I mentioned is the most effective. But yeah, changing things up is a good way to go about it, especially if you have the nerve.
Anyway, he missed, no biggie. He's playing well and we'll still win.
No, I mean the way the great penalty takers do it is they do both *at the same time*.
Le Tisser described it like this; It's impossible to miss a penalty if you do the following, it takes beyond human reactions to stop.
1) Pick a corner and be able to hit a clean, firm strike there.
2) Watch the goalkeeper as you run in he's either going to dive early or wait.
3) If he wait's it's simply not possible for him to get down into the corner for anything even remotely well struck, so you stick with your original plan, if he dives early then you just roll it into the other side of the goal.
It's the method ALL of the best penalty takers use, the ones with really good records anyway. The Shearer/Lampard/Gerrard method is better if you don't have the composure, but doing it the way Martial did is the more reliable way.
I don't know what happened with Martial, maybe he just scuffed it or thought he saw the keeper dive, but he should work on perfecting his current method rather than trying to mix it up.