We all think we're rational beings when it comes to big sales around Black Friday and Christmas, until we're in the shop grabbing those rollerblades we'll never wear or that dress that we know is hideous.

It happens to most of it, but there's a psychological reason why and most shops are happy to help us on the way to part with our cash!

Sarah Strange is a lecturer in marketing in TU Dublin and she spoke to Dermot and Dave about the psychology behind shopping.