Not long ago, I had to buy a new tyre in a hurry - the old one was puncturing like crazy because it was down to the canvas. I pulled in at the closest bike shop, bought a cheap tyre (only had cash on me, and not much at that) and that was sufficient to get me home without another flat.
Since then, I've had nothing but flats. Sometimes two in a day. The cheap tyre has given me more flats than the old one gave me in a year.
The final straw came today when a fellow cyclist (much more experienced than I) looked at the tyre and exclaimed "That's a really cheap and shitty tyre!" I had to agree, since I had changed yet another flat on the way to work this morning.
I now have an expensive, kevlar-lined tyre on the bike. The cheap, shitty one is where it belongs - in the bin.