let someone down
使某人失望
A:That's really a let-down.
A:那可真令人失望。
B:Yeah. He really does let me down.
B:是的,他确实让我失望。
A:But that should not be the reason for you to lose heart.
A:但这不应该成为你灰心的理由。
B:I'm at the end of the tether. I run out of ideas.
B:我再没有精力了,我已无计可施了。