Chain/neutral selection question

Hi
This is probably a stupid question - but here goes :redface:

I tended to have a slight issue in selecting neutral ie would jump from 1st to 2nd without giving me neutral without a bit of fiddling about.

I then noticed that the chain on my Gen 3 was slightly slack so I tensioned it correctly.

Having done that the neutral selection problem has "gone away"

My question is why as I can't see what the link is

Thanks