The German word for “disappointed” is “enttäuscht” and “Enttäuschung” for “disappointment”. This word is related to “täuschen”, which means “to deceive”.

To express “letting (someone) down”, Germans use the expression “(jemanden) im Stich lassen” – literally “let/leave someone in the stitch/sting/stab”. This expression’s original meaning is “to abandon someone during a battle”. Alternatively, one can also use “(jemanden) hängen lassen” – essentially “to leave someone hanging.”

– “Ich bin enttäuscht von dir.” – “I am disappointed in you.”
– “Es war eine große Enttäuschung.” – “It was a great disappointment.”
– “Er lässt dich nicht im Stich.” – “He won’t let you down.”
– “Wir lassen Sie nicht hängen.” – “We won’t leave you hanging.”