German phrase
Ich glaube, ich habe ~ vergessen.
Meaning
I think I forgot ___
When to use it
You think you forgot it. It sounds cautious in daily talk.
Example dialogue
Ich glaube, ich habe meinen Schlüssel vergessen.
I think I forgot my key.
Hast du ihn vielleicht zu Hause liegen lassen?
Did you perhaps leave it at home?