Sliding Doors

I went to a public health center in California for the first time in my life. I tried to walk past the automatic sliding doors, through which I saw people come out. The door just did not open to me – after trying couple of times I noticed, than the entrance was on the other side, and one should go in through a security check. I had never before visited a health center with a security check, so I did not even think about the possibility that the automatic doors did not open because of a reason (having instead noticed that sometimes the automatic doors do not work so well).