Why do we have leap-years?

So it's February 29th and we have 366 days this year instead of 365- what's the deal with Leap Years? ---------- Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow ---------- Dooblydoo thanks go to the following Patreon supporters -- we couldn't make SciShow without them!

Hacks upon hacks.   It really is amazing we are able to get anything done.   Can someone invent a metric calendar please?