Undo, and the thing you did not mean

You deleted a paragraph. Your stomach dropped. Before you rewrite from memory, try Undo. Ctrl+Z — Command+Z on a Mac — takes back the last thing you did. Type a word, undo, the word leaves. Delete a paragraph, undo, it returns. Do it again, and the thing before that returns. This lesson is that rope, Redo when you undid too far, and the moment the rope is cut: closing the window, or saving over the only copy on purpose.

Most programs keep a short memory of acts: typing, delete, paste, a format. Each Ctrl+Z walks one step back. If you undo too many times and the paragraph you wanted is gone the other way, Ctrl+Y or Ctrl+Shift+Z is Redo — walk forward again. You are on a path, not in two universes. Stop when the page looks like the one you meant. Then Save. Undo is not Save. If the light goes, undo dies with the unsaved window.

What undo will not resurrect

Empty Recycle Bin is not undone with Ctrl+Z. A file you Shift+Deleted is not in the Bin and not in undo. Replace all, if you then typed, may still undo in Word if you have not closed. A form on a website often has no undo at all. Explorer's undo — Ctrl+Z in a folder — can put a file back you just moved, once, if you have not done something else. Do not rely on it for a wedding folder. Copy, then move, as you learned.

Some programs forget after a Save, some do not. Word usually still undoes after Save, until you close. Notepad may be ruder. A browser tab's Back is not undo of a form; it may wipe the form. You have met that cousin. If you pasted the wrong thing over a selected page, undo immediately, before you click elsewhere. Selection plus paste is how whole letters vanish in one act. Undo is the next act. Then breathe.

• Open a practice letter. Type a sentence. Ctrl+Z. It should leave. Ctrl+Y. It should return.
• Select a paragraph. Delete. Undo. Confirm it is whole, not half.
• Save. Close. Reopen. Ctrl+Z should do nothing useful. That is the cut rope. The file on disk is the truth now.
• Do not practise undo on the only copy of a real certificate. Copy first.

The manners of a mistake

If undo cannot help — the window closed, the Bin emptied — stop clicking. Search, Recycle Bin, the USB, last month's backup. Rewriting in a panic makes a second bad copy. You already know the rooms. Walk them in order. A helper can look. A banner that says “restore deleted files — download now” is the virus costume. You know that door.

Undo is how a person stays calm at a keyboard. It is not bravery to refuse it. It is not a reason to skip Save every few minutes. The rope is short. The disk is the floor. Use both. Then the thing you did not mean is only a minute, not an afternoon.