Your standard is seemingly if a reliever blows ANY number of games they are never to be trusted with any big spot ever. It's hopelessly unrealistic. Odds are any shutdown reliever/big arm/whatever you want to call it they trade for or sign will, yes, blow games. It happens. The Cubs have several very good relievers, and at times they're not used as smartly as they could be used. Plus you've got a struggling offense that has left them in a ton of very close games.