When people do more reps in a row during weight training, they become worse at guessing how many more reps they could do. This means longer sets make it harder to judge your own effort accurately.

When people lift lighter weights compared to their max, it's harder for them to accurately guess how many more reps they could do, making it less reliable than when lifting heavier weights.

When people lift weights until they're almost too tired to continue, especially with arm exercises, they get better at guessing how many more reps they could do. It's like training your body to feel its limits more accurately.

In previously trained adults, lifting weights with 0–1 reps left in reserve produces the same total amount of work over five weeks as lifting with 4–6 reps left in reserve, even though the latter feels harder.

People who lift weights for over a year often guess wrong about how many more reps they can do before getting tired—they usually think they can do about 2 fewer than they actually can.

Whether you're new to lifting weights or have been doing it for years, you're just as good at guessing how many more reps you can do before your muscles give out.