The plant is pissed with you,
depending on the age and location of said leaf
...but another grows back in most accounts
...always say sorry and breathe close on it...!
It all will still grow and come out of it - marijuana is a very "hardy" plant and is hard to kill and take "abuse""mistakes". every time one grows one learns something, right
No worries, the leaf will continue to grow or drop off and be replaced by 100 or so The tops and how many will depend on the cut/strain, sometimes 2, sometimes 4. Beauty is, it won't hurt the plant, you may have to try a few different methods/cuts to get consistency, in the meantime you'll get improvements in growth just from the process. All training, whether it took "perfectly" (if there is such a thing) or not is beneficial to generating new/vigorous growth.
This one front and center, I went to pinch in veg to make a Y split and ended up taking out one whole side of the Y....So instead of the Y I got I . It got bushier down low like its supposed to just didn't grow that second top. looking at the pic you can barely tell, it had so much time to fill in the spaces . Maybe ill get a good pic of the pinched area later and post it.