What causes streaky shooting?

As to your question about streaks, I feel they are caused by a flaw in the technique, usually the "wrist flipping" thing, where the shot is powered by the smaller muscles of the wrist, hand and fingers. The source of this may be shooting at or near the top of the jump, when all you've got left as far as power is the arm, wrist and hand. If you drive or guide the ball this way, it flattens the shot for one thing, but more importantly, the muscle action is harder to control (relatively) and can also vary with the slightest thought or fear. The result is little variations in distance and direction, a little long, a little left, etc. Once you start to miss, then the fears and doubts make it harder.

I know this because I'm almost always "on." My motion is so stable and controlled, coming from large muscles, that it is very reliable. Once in awhile my mind can interfere with the simple, connected and automatic action, but it's easy to get back on track.