I have had this happen several times, but one time, a few years back was up close and really showed what an adult deer can do.
I was in a treestand in an area that has grown up recently with a type of small tree that has no growth from the ground to maybe 4 feet high, then it is very brushy. A pain to shoot thru or around, but it gives tremendous cover while the leaves are on. This was during a time when you needed to shoot a doe first, before you can get a buck.
As you guessed, I did not even SEE does for much of that year. A very nice and, till that time, never before seen by me mature buck walked into the stand of trees. He was up wind of me, never crossed my entrance path and actually walked by me at about 20 feet distance. I was maybe 12 feet up a tree and with a ton of cover.
This buck would walk maybe two or three steps, then stop and look around, UP around. He was very obviously looking at the content of the trees in the area. I got to watch him up close and personal for probably ten minutes as he walked thru my small stand of trees in the marsh, then move on over to the next stand. He was watching the entire time.
And of course, there are the does. There are a couple that like to cut thru my stand and find me. They come in together (I could see them coming, in the marsh) and then they separate, one sneaking in very slowly and watching, the other cutting down wind of the stand. They ALWAYS find me. it is a game of sorts for both of us. I will, one day, either put a mannikin in my tree with me down wind somewhere, or a second hunter down wind.
Yep, they are dumb, defenseless critters.
ChuckC