The bottom row sits below the home keys and slightly to the right. The finger goes down, the hand does not.
a → z s → x d → c f → v and b
This is the most awkward of the three rows: the finger has to curl and the little finger has the longest way to travel. This is exactly where the temptation to look down, or to grab a key with the wrong finger, appears. A wrong finger that settles in has to be unlearned later, and that is slower than getting it right from the start.
Z and X are rare letters, but C, V, B, N and M are everyday ones, so the row itself is anything but rare.
If one letter keeps going wrong, slow down for that letter only. Slowing the whole line does not fix the place that needs fixing.