I only took notice once I got 20k I was like, hang on a minute, that's a lot of people that like my stuff...
and then when I got 50k I started thinking hey, you know that play button might be possible one day...
I'm still shocked with the growth of the channel today, I've been at this for 10 years so it was easy for me to ignore the sub number.
but now I'm more aware thanks to the little play button. Because that is something to look forward to one day.
I don't see the harm on being happy about any milestone though, as long as you don't worry too much about when you hit them.