Why is February so short?

The Romans developed the calendar system we still use today. The Romans believed that even numbers (numbers ending in 0,2,4,6, or 8) are unlucky. And that's why during this time each month had either 29 or 31 days, because at this time one calendar year was only 355 days. So to create a year with 355 of days, one month had to end on an even number. And so, February was selected to be the month with 28 days.