From the Farnam Street Brain Food newsletter:
We live in a society that praises all-out effort. But giving a task 100% of your energy can lead to burnout, over-exhaustion, and injury. Jackman believes in the “85% Rule,” which means that intensity, force, or stress should never override form, technique, and preparation. Jackman elaborates: “A sprint coach realized that [Olympian] Carl Lewis did nothing at the 50-meter mark; his breathing and form was exactly the same. Other runners would try to push harder, clenching their fists, scrunching their faces. But Carl Lewis stayed exactly the same—and went on to breeze past the others.” It’s like that with everything in life — the more you try to force something, the less optimal your performance. Aim for 85% energy expenditure, and reserve the other 15% for mental & physical calm.
Further reading: This “85% Rule” Will Change Your Perception of Effort and Performance