Yeah, most people screw up by trying to get too many reps at a time.
Seriously, most people should be able to get 6, 7 or even 8 reps with 80%.
But they shoot themselves in the foot by trying to get 5 or 6 every time and crash very soon.
Let's say that you do one set every 30 seconds on the clock (e.g. start a set at 0:00, one at 0:30, one at 1:00, etc.) you get 21 sets. If you do 2 reps per set, which is more than manageable since you are 4-6 reps under your limit, you will be getting 42 reps. If you can get 3 reps per set, which should be more challenging past 8 sets you'd get 63 reps... almost nobody can get there. But a lot can get 10 sets of 3 and 11 sets of 2 which would be 52 reps... even getting 5 sets of 3, 10 sets of 2 and 6 sets of 1 would give you 41 reps and that is fairly easy to do.
You are your own worst enemy when it comes to getting a lot of total reps in.