According to Bezos, there are two types of decisions- 1) type 1 - where Bezos does not time workers' toilet breaks, and 2) type 2 - where he lets middle managers to create their own rules. It's always Day 1 :)
It's a Bezos thing. The idea is that every day is "Day 1". Just because you or your company has been around for years and years or that you've hit a major milestone, you can't rest on your laurels. You need to approach every day as "Day 1" with regard to your attitude toward innovation and moving quickly.
"It's always day one" is of Amazon's corporate slogans - I think it's something Jeff Bezos personally came up with. It's supposed to mean that every day is a learning experience... or something.