The logs were clean.

The feature mostly worked.

So we did what engineers do best.

We started reading code.

📜 The Investigation Begins

The file was massive.

• Helpers
• Extensions
• Business rules
• Edge-case handling
• Defensive checks everywhere

Over 1,000 lines of code.

We zoomed into the complex parts first —

surely the bug lived where the logic was hard.

It didn't.

😅 The Bug That Humbled Everyone

Here were the first few lines:

class PaymentManager {
    var delegate: PaymentDelegate?
    
    init(delegate: PaymentDelegate) {
        self.delegate = delegate
    }
}

Looks harmless.

No crashes.

No warnings.

No compiler complaints.

Until you notice what's missing.

💥 The Real Problem

The delegate wasn't weak.

weak var delegate: PaymentDelegate?

That single keyword.

Missing.

As a result:

• PaymentManager retained the delegate
• The delegate retained PaymentManager
• ARC couldn't break the cycle

🔁 Memory leak. Silent. Persistent. Deadly.

🤯 Why This Hurt So Much

Because everything else was… beautiful.

• Perfect abstractions
• Clean architecture
• Defensive coding
• Edge cases handled

But all of that effort couldn't save us from line 3.

🧠 The Psychological Trap

Here's what really happened:

🧠 "The bug must be in the complex logic."

🧠 "Senior code doesn't fail in simple places."

🧠 "Let's skip the boilerplate."

And that bias cost us hours.

Complexity hides bugs — but simplicity hides them better.

🧪 How We Found It (Eventually)

Not by reading deeper.

But by stepping back.

• Memory Graph Debugger
• Watching objects refuse to deallocate
• deinit never firing

deinit {
    print("PaymentManager deallocated")
}

Silence.

That silence pointed us to the top.

⚠️ The Real Lesson

Most bugs aren't:

• In algorithms
• In edge cases
• In clever abstractions

They live in:

• Initialization
• Ownership
• Lifecycles
• Defaults

Places we stop paying attention to.

🛠️ My New Review Rules

After this incident, I changed how I review code:

✅ Start from the top

✅ Scan ownership first

✅ Look for weak, unowned, lifetimes

✅ Verify deinit

✅ Never skip "boring" lines

🎯 Final Thought

We love complex bugs.

They make us feel smart.

But real-world bugs are boring.

And that's what makes them dangerous.

Next time you review code —

don't rush to line 500.

Start at line 3.