"let someone down" is correct and usable in written English.
You can use it when referring to an instance of disappointing someone, typically by not doing something they expected you to do. Example: "I'm sorry that I had to let you down by not coming to the party."
That is the greatest sin you can ever commit – to let someone down when they look to you".
Seriously, it's so much easier to let someone down now than to be stuck with their annoying habits for a whole year.
Apologise if you misbehave or let someone down but never apologise for the quality of your work – let other people criticise it first.
It's out of the question that I would let someone down on their big day, so there have been times I've had to sit up all night working.
In therapy?"' Dr. D. explained to her that that feeling -- the sense that she'd let someone down by asking for help -- was getting in the way of her recovery.
Boys, do you feel the same pressure to let someone down easily?
Do not let someone down-play your pain and minimize it, or you.
The general consensus out of the 23 interviewees was that the truth was the most dignified way of letting someone down, but everyone agreed that this had to be done carefully so as not to upset the other person.
"These were very successful women in their careers and their lives, yet almost all of them felt bad about not being married, like they were letting someone down," said Lawrence Ganong, a chairman of human development and family studies at the University of Missouri.
Letting someone down and trying to repair a relationship that you feel is kind of slipping through your hands a bit".
This is an unrealistic expectation, and as a result of this high bar that we set for ourselves, we end up letting someone down, often ourselves.
