Principle: You Aren't Gonna Need It (YAGNI)

Developers add features, abstractions, or configuration options for hypothetical future requirements that never materialize, increasing complexity and maintenance burden.

Only build what you need right now:

1. Don't add configuration for things that have one value

Bad: config.get('MAX_RETRIES', 3) when it's always 3
Good: MAX_RETRIES = 3 # Change when needed

1. Don't build abstractions for one implementation

Bad: interface DatabaseAdapter -> PostgresAdapter (only one impl)
Good: PostgresDatabase (extract interface when second impl needed)

1. Don't add hooks/plugins/events for extensibility nobody asked for

Bad: onBeforeProcess, onAfterProcess, onError hooks everywhere
Good: Simple function that does the thing

1. Don't future-proof APIs

Bad: version: 1, _reserved: null, metadata: {}
Good: Just the fields you need today

1. Don't optimize before measuring

Bad: Caching layer added 'in case it's slow'
Good: Measure first, optimize the actual bottleneck

Exception: Security and data integrity ARE worth building proactively.
You do need input validation, proper auth, and data backups from day one.

Every feature you build has ongoing maintenance cost. Features built for hypothetical needs are pure cost with no realized benefit.