Intermediate back attack set up
I think one of the reasons many new students struggle with attacks is that they skip or rush the set up. This makes perfect sense to me. The Jiu Jitsu learning curve is steep and filled with failure. You spend much of your time trying to escape inferior positions. It takes some mat time and experience to get to an attacking position in live training. So the first few times you find yourself on someones back it makes sense that you would be in a hurry to get a finish.
The experienced Jiu Jitsu player knows that there are a few sweet spots for attacking: 1) when it isn't expected and 2) when you are so far ahead of the other player that resistance is futile. If you set the attack up AS you are obtaining the back then you have a good chance of finishing. If however you end up on the back and your partner has time to fortify defenses, then you need to go with plan B, degrade your partners position until they are not left with a reasonable defense.
Here is one way of approaching plan B when you have secured the back position
The above example is acceptable however sometimes plans don't follow the script. It would be ideal if you obtain the back and then finish, but sometimes your partner has a better defense than your offense.
Attacking isn't a one and done venture, it is ongoing story where you concede the attempted escape prior to it being completed. You can regain the initiative and continue attacking if you respect the escape attempt earlier rather than later, and use the opportunity to attack again.
Mental barriers to attacking
Numerically, a finish is one (singular) thing, (an armbar, a choke). It is an end point. When you are beginning Jiu Jitsu the frame of reference you often have is dependent upon that idea, "he was finished with A choke". So when the new student is attacking, they often attack that one thing as if it is the only thing, (and with 100% effort). More experienced practitioners know that when you are attacking you are not working on a singular thing. You should be attacking with a few different attacks at the same time, (with much less effort).
The choke attempt usually degrades your partners position leaving the arm open to attack. While I am attacking I am not betting the farm on any one attack, I am working on two or three related attacks simultaneously and trying to read my partners response. So while a finish may end as one thing it begins as two or three. Keep that in mind as you are working on offense. You are looking for the open window, not trying to smash through the closed one.