He came in for help after his attempts to stop smoking by willpower alone failed.

他仅靠毅力戒烟失败后到这里来求助。

《柯林斯英汉双解大词典》

For then we will realize that our lives are not controlled by the whims of fate, but by ourselves, by our own actions, and by our own willpower.

因为到那时我们就会意识到，我们的生活不是由莫测的命运控制的，而是由我们自己、我们自己的行动和我们自己的意志控制的。

youdao

You can end up wasting a lot of energy by pushing yourself on by sheer willpower... when, in fact, it may be the case that your brain and body really need a break.

纯粹用毅力勉强自己工作，最终你只会浪费很多精力. .而这时候实际上是你的大脑和身体都真的需要休息一下了。

youdao

The Dragon Boat Festival is a custom seemingly kept going by willpower, surrounded by the remains of a great tradition of endeavour.

BBC: Here be dragons

While some experts argue that people who are obese should simply eat less and exercise more, many physicians who treat obesity say it is driven by biological changes in the body, not lack of willpower.

WSJ: New Diet Pills Offer Option to Off-Label Obesity Drugs

When your brain detects a discrepancy, it reacts by throwing resources at it: attention, effort, deeper processing of information, and willpower.

FORBES: How to Become A Great Finisher