Feeling discouraged with

気(き)を落(お)とす means to lose heart or become discouraged after bad news, a setback, or a disappointment.

Literal Meaning

This expression literally translates as “to drop one’s spirit/energy”. The word 気(き) represents one’s spirit, energy, or mood, while 落(お)とす means to drop or let fall.

Usage Notes

The phrase often appears as 気を落とさないで, “don’t be discouraged” or “cheer up”, when comforting someone who feels defeated.

Examples

Feeling discouraged after being turned down for a job with 気を落とす

Manga panel from ハクメイとミコチ showing example of Feeling discouraged after being turned down for a job with 気を落とす.
ハクメイとミコチ » Volume 2 » Page 71

Hakumei hoped to help with a stone wall restoration, but the repair guild’s chairman refused her, saying she wasn’t needed for the project.

イワシ:
「なあ ハクメイ。 そんなに気(き)を落(お)とすなよ」
“Hey, Hakumei. Don't be so down.”
ハクメイ:
「落(お)としてない」
“I'm not down.”