Do you know what maximum effort means, entails, looks, and feels like? Most gymgoers don't!
Doing a set of 5 repetitions is different to doing 10 reps, 15 reps, or heaven-forbid 20+ reps.
You need to adjust the weight up/down or alter the intensity by making it easier/harder.
BUT...it always demands your 100% effort, regardless of the exercise or how many reps you are performing.