Not a daft question at all. For most of my many years of sewing, I would always head to shops or market clutching my latest pattern, and buy pretty much exactly what it said.
You still end up with plenty leftover, as pattern layouts are never very economical.
Fast forward MANY years, and I found The Sewing Forum[precursor of this site]. There I learned about stash, about buying on impulse for the hell of it, and only matching patterns and fabric by chance.
Naughty TSF!
Basically, as so many answers, 'it depends'
It depends on your size, your skill in eking something out of nothing, fabric width, and on your favoured styles and shapes of garments. If in doubt, hunt something out on t'net and look at yardages.
I tend to buy 2 or 3m depending on intention, price, and impulse. Some of my historical makes demand greater yardages, but for 'normal' clothes that's ample. For simple tops or shortish skirts, you can get away with just 1m.
A while back someone produced a guide to 'how much fabric to buy' I bet if you google you'll find it