What do you guys think about Descartes' argument? What's the critical value about this thought?

it reminds me of my sister..she doesn't trust her own judgement on anything so when we go shopping,she HAS to bring our aunt,whom for her has "perfect" fashion sense. if our aunt told her to buy an item,she immediately pays for it but if she has to buy something for herself,we'd go around the mall for hours and come home empty-handed.