Bug #1 — The Clock That Kept Slipping

Sun, 02 Aug 2026 09:00:00 +0300

I was integrating an external API. The datetime it stamped on every response never agreed with my local clock — and not by a clean, constant amount. Sometimes it was 4 minutes behind. Later, 8. Then more. The gap kept drifting.

  our clock          their timestamp       gap
  ─────────────────────────────────────────────
  10:14              10:10                 −4 min
  11:02              10:54                 −8 min
  13:40              13:29                 −11 min
                                            ↑
                            not a constant — it grows

The Wrong Theory

My first instinct was that we were sending the wrong value, so I checked the payload. The date was correct. That check cost me time: a timezone shift usually leaves the date component intact and only moves the clock, so a date-only comparison passes while the instant is wrong. The date only flips when the shift crosses midnight — which is why “the date is right” feels like evidence and isn’t.

Root Cause

Mon, 01 Jan 0001 00:00:00 +0000

Notes and highlights from reading Root Cause by Hussein Nasser — war stories from twenty years of backend bugs, and what each one taught.

Debugging on Mike Mwita

Bug #1 — The Clock That Kept Slipping

The Wrong Theory

Root Cause