They
are small like another poster mentioned, but their big primary eyes and their behavior makes them seem a lot less threatening than other spiders as well. For example, if they notice you they tend to reposition themselves to get a better look at what you are. They are also pretty rare to find indoors, which means you're not likely to be surprised by them while brushing your teeth or taking a shower.
[1] https://www.youtube.com/watch?v=apWeH2f_uao