If the valve is completely stuck or you live in an apartment where the main valve is behind a locked door, wave the white flag. Call a plumber or your landlord.
How To Turn Off Water To Your House: Todays Sunday Skill
Also, if you ever feel unsafe—like gas is involved or the water is near electricity—get out and call a pro. Your safety is worth more than a dry floor.
Remember: knowing where the shut-off is already makes you the cool, prepared person in your friend group. You get the “I’m not panicking” badge.