I'll work hard. I don't want to let him down.

我会努力工作。我不想让他失望。

《柯林斯英汉双解大词典》

The student let him down, opened the sack, and set him free.

书生放他下来，打开口袋，放了他。

youdao

Next day the old woman took him to the well, and let him down in a basket.

第二天，老婆婆带他到井边，用篮子把他放了下去。

youdao

Let him inform the human race that it came down from the trees.

VOA: standard.2009.11.25

"He's too good a pitcher to let adversity behind him let him down, " Johnson said.

NPR: Strasburg Drops To 1-5 As Cubs Beat Nationals 8-2

How he had trusted me, encouraged me, had high hopes for me, and I had let him down.

NEWYORKER: Hand on the Shoulder

Too often, his fiery temperament has let him down and tonight he let down the blue half of Manchester.

BBC: Europa League as it happened