The reason I do not open my incubator any more until the hatch day has past is years back when I did that, seemed most of the unhatched eggs would not hatch about every time. My mother had the same problem, my step sister, several of my friends all had the same problem. Then I started just leaving them in until the day after the hatch date and I had some good hatches. Then I shared this with my Mother and everyone and they to let them stay in and they two had great hatches, for many hatches----some friends to this day still hatch a few times a year and still have good hatches---leaving them in.
OK after getting on this forum----I have found out that a lot say they have good hatches opening at will!! So my conclusion is---Location----got to be. Maybe if I did like some and opened at will then become a hands-on-hatcher---help the ones that need it----maybe I would have a lot better hatches than I did years back when I opened at will?? Not sure?? I know now---I do not have to open to help---I just let them sit tight until its time to open and take all out----which most of the time that number will be close 100% hatch.
When a Newbie doesn't feel comfortable opening---I just let them know I have a better hatch leaving it closed.
What I have found out on here is that a newbie with no experience has a lot better luck just leaving everything closed than a newbie that opens all the time. So I never suggest to a newbie to open and remove at will----if they feel comfortable at it--its their incubator.
The ones that open at will and have great hatches----that's Good---continue doing what works---that's What I do.