Meaning trap

let down

be the weak point

To make something less effective, impressive, or successful than it could be, often by being a weak or disappointing aspect of it.

phrasal verbC1occasional

Don't mix these meanings

Same phrase, different job.

be the weak point

To make something less effective, impressive, or successful than it could be, often by being a weak or disappointing aspect of it.

let down (disappoint someone)

'let down' also has the more basic meaning 'disappoint someone'; this is the advanced sense.

Notice where the phrase sounds natural.

The film was visually stunning, but the weak script really let it down.

While the research was thorough, the lack of clear conclusions let the paper down and weakened its overall impact.

One small grammar move makes it sound right.

Not: The film was let down ~~for~~ the bad acting.

Say: The film was let down by the bad acting.

In the passive, the weak element takes 'by' — 'let down by X'.

Tap the one a native speaker would say.

Words that usually travel with it.

let + down

Other meanings and phrases to compare.

let down (disappoint someone) — 'let down' also has the more basic meaning 'disappoint someone'; this is the advanced sense.