"What's the status of the new SuperParser function?" asks your project manager.
"Oh, it's 90% finished, I'm just trying to figure out a few minor issues" you say.
Unfortunately, you've said this every week for the last 3. Before that, it only took you a week to get to so-called 90% completion.
What's wrong with this picture? Are you wrong for thinking you're almost done? Of course not, but