I've always put a lot of stock in common sayings/perceived wisdom. There's a reason they've lasted through the ages.
It's interesting when you hear one that's new to you.
A little while back I was talking about the price of something, dismissing something like an extra 20 quid by buying in one place versus another.
Anyway, bloke tells me "it's not a lot of money, but it's lot when you don't have it!"
Now, whether this even counts as a "saying" or not, I think it's very clever.
It's easy to say 5 euro isn't a lot of money, but try buying something for a fiver less in a shop and you'll find out sharpish how important they think it is

"it's a lot when you don't have it". Nice! Makes you think twice about wasting money, even small amounts.
Any others that mightnt be well known?