2nd/10_Wiki/Topics/Backend/KISS (Keep It Simple, Stupid).md

---
id: wiki-2026-0508-kiss-keep-it-simple-stupid
title: "KISS (Keep It Simple, Stupid)"
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [KISS Principle, Keep It Simple]
duplicate_of: none
source_trust_level: A
confidence_score: 0.95
verification_status: applied
tags: [principle, design, software-engineering]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: any
  framework: any
---

# KISS (Keep It Simple, Stupid)

## 매 한 줄
> **"매 simplest-thing-that-could-possibly-work"**. 매 1960s Lockheed Skunk Works 의 Kelly Johnson 의 aerospace heuristic → 매 software 매 universal 의 design principle. 매 sibling: YAGNI, Worse-is-Better, Occam's Razor.

## 매 핵심

### 매 mechanism
- 매 each abstraction 의 cognitive cost 의 measure.
- 매 minimum-viable design → 매 iterate.
- 매 complexity 매 emergent, never additive cheap.

### 매 forms
- **Code**: fewer lines, fewer abstractions, fewer dependencies.
- **API**: fewer endpoints, fewer params, fewer states.
- **System**: fewer services, fewer protocols, fewer config knobs.

### 매 응용
1. Pre-mature abstraction avoidance (Rule of Three).
2. Boring-tech preference (PostgreSQL > custom DB).
3. Monolith-first (Fowler), microservices later if needed.

## 💻 패턴

### KISS 매 too-complex (anti)
```ts
// Over-engineered: factory + builder + strategy for "add 2 numbers"
class AdderFactory {
  static create(strategy: AddStrategy): Adder { /* ... */ }
}
```

### KISS 매 right
```ts
const add = (a: number, b: number) => a + b;
```

### Service split: simple-first
```ts
// Simple: 1 service, postgres
app.post('/order', async (req, res) => {
  const order = await db.orders.create(req.body);
  await sendEmail(order);
  res.json(order);
});

// Only when justified by load/team-size: split into microservices.
```

### Dependency minimalism
```bash
# package.json 매 audit — every dep is liability
npm-check --unused
depcheck
```

### Config 매 default-driven
```ts
// Bad: 27 required env vars
// Good: smart defaults, override only when needed
const PORT = process.env.PORT ?? 3000;
const DB_URL = process.env.DATABASE_URL ?? 'postgres://localhost/dev';
```

### Naming for clarity
```ts
// Bad
function p(d: any[]) { /* ... */ }

// Good
function paginate(items: Item[]): Page<Item> { /* ... */ }
```

## 매 결정 기준
| 상황 | Choice |
|---|---|
| First version | Simplest possible, single file if needed |
| 매 second feature 의 same shape | Still don't abstract |
| 매 third 의 same shape (Rule of Three) | Now abstract |

**기본값**: Inline the code. Abstract only when 매 third 의 same pattern emerges.

## 🔗 Graph
- 부모: [[Software-Design-Principles]]
- 변형: [[YAGNI]]
- Adjacent: [[Premature-Optimization]] · [[Rule of Three]]

## 🤖 LLM 활용
**언제**: design review, architecture decision, code review (cut complexity).
**언제 X**: 매 inherent-complexity domain (compilers, crypto, distributed consensus) 매 simplification 매 wrong-target.

## ❌ 안티패턴
- **Premature abstraction**: 1 use 의 abstraction 매 wrong shape.
- **Configuration explosion**: every-flag-as-knob.
- **Microservices day-one**: 매 distributed monolith 의 invitation.

## 🧪 검증 / 중복
- Verified (Kelly Johnson — Lockheed Skunk Works; Rich Hickey — Simple Made Easy talk; Worse-is-Better essay).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — KISS FULL content with anti-patterns |