Protect sheet in Excel

This is the layer that turns a validated sheet into a durable one. It hinges on a single fact that almost everyone gets backwards at first.

Every cell has a Locked property, and it's ON by default, but it does nothing until the sheet is protected. The lock just waits. You can format cells as locked or unlocked all day and see no effect, because the property only bites the moment you protect the sheet. Protecting a sheet means "from now on, locked cells can't be edited, and unlocked cells still can." Since every cell starts locked, protecting a fresh sheet freezes the whole thing, which is almost never what you want.

How do you protect a sheet step by step?

So the correct workflow runs in this order, and the order matters:

1. Select the cells the user is allowed to edit, the input cells of your form, and unlock them. Go to Home ▸ Format ▸ Format Cells ▸ Protection and untick Locked. Ctrl+1 opens Format Cells directly. These are now the only cells that will stay editable.
2. Leave every formula, label, and reference cell locked (they already are).
3. Now protect the sheet with Review ▸ Protect Sheet (Alt, R, P, S). You can set a password if you like. More important is the checklist of allowed actions, such as selecting locked cells, formatting cells, sorting, using AutoFilter. That list decides what a user may still do inside the protection.

Unlock first, then protect. Do it the other way round, protecting the sheet before unlocking your input cells, and you've locked yourself out of your own form. The input cells are still locked by default, and now the sheet enforces it. The fix means unprotecting, unlocking, then re-protecting. This inverted order is common mistake #4, and it's the most frequent "why can't I type in my own spreadsheet?" support question there is.

What else does protection cover, and why pair it with validation?

Two neighbouring tools complete the picture. Protect Workbook (Review ▸ Protect Workbook) is a different lock. It protects the workbook's structure, stopping users from inserting, deleting, renaming, hiding or reordering sheets, and it leaves the cells within them alone. A cell can also be set to Hidden on the same Protection tab. Once the sheet is protected, the formula in that cell disappears from the formula bar while the result still shows. That's handy when you want to share a model without exposing its proprietary calculations.

Which brings you back to the paste problem. Data validation doesn't stop a paste, so you make validation actually enforceable by protecting the sheet. Then the validated input cells can't be overwritten by a paste that carries its own (absent) validation. Validation says what belongs, and protection makes that saying stick.