Check out https://www.reddit.com/r/TFABLinePorn/

A subreddit where users post positive or probably positive pregnancy tests.

Pregnancy tests generally measure hCG concentration in urine, early in the pregnancy concentrations are low and the test line will be very faint if visible at all. It's only later on in the pregnancy when the line will become more visible.

Pregnancy also involves a lot of emotion, hope & fear, in combination it's not that surprising that a portion of people misread pregnancy tests.