Issue 12 | Understanding "Memory Lapse": Vibe Coding Failure Post-Mortem Analysis

Updated on 4/5/2026

🎯 Learning Objectives

By the end of this issue, you will understand:

  1. Why "Vibe Coding," while exhilarating, often leads to project collapse
  2. The physical limitations and memory loss mechanisms of Claude Code's context window
  3. Five typical failure scenarios and their corresponding prevention strategies
  4. How to balance "the thrill" and "engineering discipline"

📖 Core Concepts Explained

12.1 What is Vibe Coding?

Vibe Coding Definition (by Andrej Karpathy):

"You completely give up on trying to understand the code yourself,
fully hand it over to the LLM, embrace the exponential acceleration,
see something wrong and just say 'fix it',
and then iterate wildly until...
'it works' or 'it completely breaks'."

Core Characteristics:
  ✅ Extreme speed
  ✅ Low barrier to entry (no deep code understanding required)
  ❌ Zero predictability
  ❌ Unable to revert to a known good state

12.2 Why Does Claude "Forget"?

The Essence of the Context Window:

╭──────────────── 200K Token Window ──────────────────╮
│                                                    │
│  [System Prompt] [CLAUDE.md] [Your Chat History]   │
│                                                    │
│  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■□□□□□□□□□□          │
│  └─── Occupied ~75% ───┘ └── Remaining Space ──┘   │
│                                                    │
│  When the window is full:                          │
│  → The earliest chat content is truncated          │
│  → Claude forgets what you did in round 1          │
│  → It might reinvent functions already written     │
│  → Or overwrite previously designed logic          │
│                                                    │
╰────────────────────────────────────────────────────╯

12.3 Five Typical Failure Scenarios

Scenario 1: Goal Drift ━━━━━━━━━━━━━━━━━━━
  Round 1: "Make a Todo App"
  Round 5: "Add a user system"
  Round 10: "Integrate payment functionality"
  Round 15: Claude thinks it's building an e-commerce platform
  ❌ Result: The codebase becomes an incomprehensible Frankenstein's monster

Scenario 2: Over-editing ━━━━━━━━━━━━━━━━━
  You: "This button style is wrong"
  Claude: Rewrites the entire component tree
  ❌ Result: Fixed the button, broke the navigation

Scenario 3: Retry Loop ━━━━━━━━━━━━━━━━━━━
  "Tests failed" → Fix it → "Still failed" → Revert
  → Fix again → Broke more things → "Let's rewrite everything!"
  ❌ Result: Consumes a lot of tokens, spinning in circles

Scenario 4: Phantom Dependencies ━━━━━━━━━
  Claude created utils/helper.ts in Round 3
  In Round 20, it forgot this file existed
  And recreated a functionally identical utils/tools.ts
  ❌ Result: Duplicate modules appear in the codebase

Scenario 5: Confidence Inflation ━━━━━━━━━
  Claude: "I have fixed all issues ✅"
  In reality: It only fixed the parts it remembered
  ❌ Result: Hidden bugs explode in production

💻 Simulating Claude TUI Interaction

Scenario: Real-World Failure — Goal Drift

╭─ Round 1 (All normal)─────────────────────────────╮
│                                                    │
│  > Help me create a Markdown editor                │
│                                                    │
│  Claude: Okay! I'll create a React-based           │
│  Markdown editor using CodeMirror...               │
│  ✅ Created 5 files, all normal                    │
│                                                    │
╰────────────────────────────────────────────────────╯

╭─ Round 8 (Starting to deviate)─────────────────────────────╮
│                                                    │
│  > Add real-time collaborative editing functionality │
│                                                    │
│  Claude: I'll integrate Y.js for CRDT synchronization... │
│  ⚠️ Modified 12 files                              │
│  ⚠️ Introduced WebSocket Server                    │
│  ⚠️ Architecture complexity jumped two levels      │
│                                                    │
╰────────────────────────────────────────────────────╯

╭─ Round 15 (Completely out of control)────────────────────────────╮
│                                                    │
│  > The editor is showing a blank screen, fix it    │
│                                                    │
│  Claude: 🔍 Let me see...                          │
│  (At this point, Claude has forgotten the original architecture from Rounds 1-5) │
│  (It rewrote App.tsx, overwriting the CodeMirror configuration) │
│                                                    │
│  Claude: ✅ It should be fixed!                    │
│                                                    │
│  Actual result: The editor displays, but collaborative functionality is completely broken │
│                                                    │
│  💀 Project enters a "fix one, break two" death spiral │
│                                                    │
╰────────────────────────────────────────────────────╯

Correct Approach: Preventing Failures with Engineering Discipline

╭─ Failure Prevention Checklist ────────────────────────────────────╮
│                                                    │
│  ✅ 1. Execute /compact every 5 rounds of conversation │
│         Compress context, retain key decisions     │
│                                                    │
│  ✅ 2. Record architectural invariants in CLAUDE.md │
│         "Editor core is based on CodeMirror 6,     │
│          do not replace with other libraries"      │
│                                                    │
│  ✅ 3. git commit before every major change        │
│         "Commit the current stable version before adding collaborative editing" │
│                                                    │
│  ✅ 4. Limit the scope of changes for a single prompt │
│         "Only modify files under src/editor/,      │
│          do not touch src/server/"                 │
│                                                    │
│  ✅ 5. Use task_plan.md to track progress          │
│         Let Claude know "what we are doing,        │
│          and what has been completed"              │
│                                                    │
╰────────────────────────────────────────────────────╯

💻 Code Demo: Practical Tools for Failure Prevention

# ✅ Regularly compress context (the most important failure prevention method)
# Type in the conversation:
> /compact

# ✅ Set up context usage monitoring
# Add to CLAUDE.md:
cat >> CLAUDE.md << 'EOF'

## Engineering Constraints
- Do not modify more than 3 files at a time
- git commit current state before modifying
- Run npm test immediately after modifying
- If tests fail more than 3 times, stop and report the issue
EOF

# ✅ Checkpoint before starting new features
claude "Before starting a new feature:
  1. git status to confirm the current working directory is clean
  2. List the core file structure of the current project
  3. Then start [new feature description]"

# ✅ Use Plan Mode to preview changes first
# Press Shift+Tab in the terminal to switch to Plan Mode
# Claude will describe what it intends to do, but will not actually execute it

🔧 Involved Tools / Commands

Tool/Command Failure Prevention Use Description
/compact Compress context Prevents memory loss due to token overflow
/clear Clear conversation Restarts from a completely clean state
Shift+Tab Switch mode Preview changes in Plan Mode before execution
CLAUDE.md Persistent memory Records core project constraints and architectural decisions
git commit Checkpoint Ensures a revertible state before every major change

📝 Key Takeaways from this Issue

  1. Vibe Coding is thrilling but dangerous — without constraints, failure is inevitable
  2. Claude's context window has physical limits, long conversations inevitably lead to forgetting
  3. Goal Drift and Over-editing are the two most frequent causes of failure
  4. Use /compact to regularly compress, and CLAUDE.md to solidify constraints
  5. git commit before every major change is the simplest and most effective safety net

🔗 References