Occam's Razor
The simplest explanation is usually the correct one.
Explanation
When you're trying to figure out why something happened and you have multiple possible explanations, the simplest one is usually correct. Named after medieval philosopher William of Ockham, this principle helps prevent overthinking. It doesn't mean complex explanations are always wrong, but you should rule out simple explanations before considering complicated ones.
Real-World Example
Your website crashes at 3pm daily. Complex theory: Sophisticated DDoS attack timed to business hours. Simple reality: That's when the daily backup runs and maxes out server resources. Netflix's 2008 outage wasn't hackers or distributed system failure—someone accidentally deleted a semicolon in a config file. Your coworker isn't responding to emails—they're not plotting against you, their spam filter caught your messages.
How to Apply
Debug checklist: 1) What changed recently? (90% of issues) 2) Are basic resources OK? (disk, memory, network) 3) Did someone make a typo? 4) Is an external service down? Only after exhausting simple causes should you investigate complex scenarios. When designing: Start with the simplest solution that could possibly work.