Technical Debt: Why Every Debt Must Be Repaid

1. What is Technical Debt?

1.1 Origin

Technical Debt was introduced by Ward Cunningham in 1992.

Like financial debt, compromises made to meet deadlines also generate “interest”.

1.2 Analogy

Financial debt:
Borrow 1M → Buy house → Live → Repay principal + interest

Technical debt:
Ship quickly → Code compromise → Temporarily OK → Later hard to change + higher maintenance cost

1.3 Manifestations

Explicit debt:

Code without tests

No documentation

Inconsistent naming

Duplicate code

Implicit debt:

Inflexible architecture design

Unreasonable technology choices

Chaotic dependencies

Complex deployment

2. Sources of Technical Debt

2.1 Deliberate debt

Scenario: To meet launch, deliberately skip things
"Launch this feature first, add tests later"
"This code works for now, will refactor later"
"Skip API docs, ship feature"
Consequences: debt created

Characteristics of deliberate debt:

Know where the risk lies

Plan subsequent repayment

Assess the interest

2.2 Unconscious debt

Scenario: Unaware of debt
"This code looks fine"
"This architecture is perfect"
"No need for tests, I'm confident"
Consequences: debt accumulates silently

Characteristics of unconscious debt:

Unaware of risk

Code quality is low

Lack of best practices

2.3 Classification (converted from table)

Sources and examples:

Time pressure – rushing, no time for tests

Lack of skill – using bad designs

Insufficient communication – misunderstanding requirements, rework

Architecture decay – layered patches

Technology evolution – legacy code

3. Interest of Technical Debt

3.1 Forms of interest

Interest = increased maintenance cost + reduced development efficiency + more bugs

Examples:

No automated tests → fear of affecting other features when changing

Duplicate code → need to modify many places

Inconsistent naming → more time to understand code

Inflexible architecture → harder to add new features

3.2 Simple calculation

Total cost = Initial cost + Σ(Debt interest × time)

Example:
- Initial cost: 1M
- Debt amount: 0.2M
- Annual interest rate: 30%
- 2 years unpaid: Total = 1 + 0.2 + 0.2×30%×2 = 1.12M
- 5 years unpaid: Total = 1 + 0.2 + 0.2×30%×5 = 1.30M

3.3 Out‑of‑control case

Year 1: Debt 10%
Year 3: Debt 30%, development efficiency down 50%
Year 5: Debt 60%, new features cannot be released, team collapses

4. Managing Technical Debt

4.1 Identification

Code level:

Code review

Static analysis tools

Test coverage

Architecture level:

Architecture review

Code complexity analysis

Dependency analysis

Debt inventory (example):

# Technical Debt List

| ID | Description | Location | Severity | Interest cost | Fix suggestion |
|----|------------|----------|----------|--------------|----------------|
| TD001 | No unit tests | user module | High | 2 person‑days/feature | Add tests |
| TD002 | Duplicate code | common module | Medium | 0.5 person‑days/feature | Refactor |
| TD003 | Inconsistent naming | global | Low | 0.1 person‑days/feature | Rename |

4.2 Prioritization

Evaluation dimensions:

Interest cost – how costly the debt is to ignore

Repayment cost – effort required to fix

Risk level – likelihood of problems

Priority matrix:

High interest + low repayment → repay immediately
High interest + high repayment → plan repayment
Low interest + low repayment → fix when convenient
Low interest + high repayment → defer

4.3 Repayment strategies

Strategy 1: Reserve time

Allocate 20% of each sprint to debt work
Sprint 1: 80% feature + 20% debt
Sprint 2: 80% feature + 20% debt
Sprint 3: 80% feature + 20% debt

Strategy 2: Incremental refactoring

Do not try to clear all debt at once; improve gradually
Stage 1: Stop bleeding (fix bugs)
Stage 2: Improve (add tests)
Stage 3: Refactor (redesign)

Strategy 3: Replace old debt with new, lower‑interest debt

Swap a bad architecture for a better one
New architecture = new technical debt, but with lower interest
Applicable when fully re‑architecting a legacy system

4.4 Prevention

Measures:

Code standards – unified coding guidelines

Code review – gatekeeping

Automated testing – ensure quality

Technical planning – avoid impulsive choices

Debt awareness – whole team recognizes debt

5. Technical Debt Practices

5.1 SonarQube scanning

# Install
docker run -d --name sonarqube -p 9000:9000 sonarqube

# Scan project
sonar-scanner -Dsonar.projectKey=myproject

Sample report (excerpt):

# Code quality report

| Issue type | Count | Severity |
|-----------|-------|----------|
| Bug       | 15    | High     |
| Vulnerability | 3 | Critical |
| Code smell | 200   | Medium   |
| Duplicate code | 5% | Medium |
| Coverage   | 35%   | Low     |

Recommendations:
1. Fix the three vulnerabilities first
2. Add unit tests to raise coverage
3. Refactor duplicate code

5.2 Debt‑governance workshop

1. Collect debt (30 min)
   – Each person lists three debts
   – Record on whiteboard

2. Evaluate debt (30 min)
   – Assess interest cost
   – Assess repayment cost

3. Set priority (20 min)
   – Draw debt map
   – Choose top 5

4. Plan (20 min)
   – Assign owners
   – Define timelines

5.3 Debt‑governance OKR

# Q1 Technical Debt Governance OKR

Objective: Reduce technical debt, improve development efficiency

Key Results:
- Raise test coverage from 35% to 60%
- Fix all critical bugs (15)
- Refactor three duplicate‑code modules
- Write documentation for five core modules

6. Common Misconceptions

6.1 Myth: Zero debt

Wrong belief: aim for zero debt.

Correct view: debt is inevitable; the goal is to manage it.

Perfect code takes too much time

Fast‑changing business creates debt

Some debt accelerates delivery

6.2 Myth: All debt is bad

Wrong belief: technical debt is always a problem.

Correct view: intentional debt can be a strategic choice.

Quick market entry may justify shortcuts

Validating a business model is paramount

Technical debt can be a time‑buying token

6.3 Myth: One‑off elimination

Wrong belief: wait until debt piles up then refactor.

Correct view: continuously manage debt.

Debt compounds

Refactoring risk is high

Can damage team morale

7. Summary

Key points: Technical debt is a compromise made for speed, it incurs interest in the form of higher maintenance cost and lower efficiency. Management follows the flow → identify → prioritize → repay → prevent. Common pitfalls include chasing zero debt, treating all debt as harmful, and trying to eliminate it in a single effort. The guiding principles are to keep debt conscious, prevent unconscious debt through standards, manage it continuously, and balance the trade‑offs because moderate debt can accelerate business.