Let me break it down for you if you still don't get it.
This is the beginning of the decade. I can prove it...
The decade (which is 10 years... you do know that, right?).... the decade of the 90s STARTED in 1990 and ended with 1999.
Go ahead. Count them out.
There's 10 there.... count them.... COUNT THEM!
That means that the next decade STARTED with 2000 and ENDED in 2009. We are starting a new decade.
Yes, I know that zero is not a counting number, but it doesn't apply here. A decade is a length of time....
When my son celebrated his 10th birthday, he was celebrating being alive for a full decade, NOT celebrating starting the last year of that decade.
Do you get it?
I'm glad I got that off my chest.