Top 3? That's asking for a full confession.
First one that still stings - spent a week writing a sales page for a launch. Perfect hook. Killer body. Then realised I'd been optimising for a landing page that didn't have a buy button. Just a newsletter opt-in. Client hadn't told me the product wasn't ready. I'd sold air.
Second - ran a Facebook campaign targeting "dog lovers". For a high-end mattress company. Thought I was being clever with lookalikes. Spent five grand. Got a ton of cute puppy pics in the comments. Zero sales.
Third - sent an email blast with a personalisation tag that didn't merge. Every single recipient saw "Hey {FirstName}, check this out". Open rate was... not great.
You're not the worst. You just haven't hit rock bottom yet.