knicken
to fold
To bend something, usually paper or cardboard, so that a sharp crease or break is formed.
Bitte knicke die wichtigen Dokumente nicht, sondern rolle sie.
Please don't fold the important documents; roll them instead.

to fold / bend
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to fold
To bend something, usually paper or cardboard, so that a sharp crease or break is formed.
Bitte knicke die wichtigen Dokumente nicht, sondern rolle sie.
Please don't fold the important documents; roll them instead.

The verb 'knicken' is closely related to the noun 'der Knick' (bend, crease). A 'Knick' is the result of the action: a crease, a bend, or a breaking point.
Nach dem Sturm war ein deutlicher Knick im Baumstamm zu sehen.
After the storm, a clear bend could be seen in the tree trunk.
The perfect tense of 'knicken' can be formed with 'haben' (to have) or 'sein' (to be), which changes the meaning slightly. With 'haben', the active action is emphasized; with 'sein', the state or result is emphasized.
Er hat den Brief aus Versehen geknickt.
He accidentally folded the letter.
The object of the verb makes the meaning clear. With flat, thin things like 'Papier' (paper), 'Foto' (photo), or 'Karton' (cardboard), 'knicken' means to fold or crease. With long, rigid things like 'Ast' (branch), 'Blume' (flower), or 'Zweig' (twig), it means to break or snap.
Wer hat die Seite in meinem neuen Buch geknickt?
Who folded the page in my new book?
The colloquial expression 'etwas knicken können' has a fixed structure with the modal verb 'können' (can). It expresses that a plan or hope has to be given up.
Den Ausflug am Wochenende können wir bei diesem Regen wohl knicken.
With this rain, we can probably forget about the weekend outing.
to forget
'vergessen' and 'etwas knicken können' can seem similar in certain colloquial situations. 'Vergessen' normally means that you no longer remember something. In commands like 'Vergiss das!' (Forget it!), it can also mean: don't keep thinking about it. 'Das kannst du knicken' is a fixed colloquial expression and means: the plan is hopeless or not possible. Learners may confuse this because both sentences sometimes express that you should give up a thought or plan. For actual remembering, use 'vergessen'; for a plan with no chance, 'knicken' is very colloquial.

Den Termin ohne Antrag kannst du knicken, sagt der Chef nach dem Gespräch.
You can forget about the appointment without an application, the boss says after the meeting.
Wir vergessen nach der Pause oft, was noch auf der Einkaufsliste steht.
After the break, we often forget what is still on the shopping list.