If your bike is anywhere near any building work, or a skip, you have to be extra observant about what's around your bike on the floor.
These were the reasons for my last two punctures, one at work and one at home.
My neighbour's were having work done and the amount of screws and nails dropped and not cleared up properly was a joke.
And at work they plonked a skip near to where i park my bike every day, but not once did they clean up around it at any time, but i'm a lot wiser now to both scenarios.