Arduino vs 555 reliability

Also, your reality does not figure the whole lifecycle of the part. You are not considering the failures of parts that happened before whatever the product is shipped off the factory floor. Sometimes the failures are catastrophic, and other times they are latent (ticking time bombs - these are the failures that really suck). Reworking a board lowers the reliability of the parts on it - even innocent bystanders. There is no getting around it. In my metal film resistor example, having them on a board will statistically lower the reliability of surrounding components, because some amount of those resistors will be either flawed rework, and will cause damage to some number of components that are mounted nearby. Those tiny resistors and caps can be real pains sometime, so every manufacturing engineer is happy to see when they go away. Yield killers, basically. -- Will