Personally I don't find it hard to put stickers on things because I am worried about being silly, but I find defacing an otherwise clean object difficult. Like getting a brand new car or phone and trying very hard not to get a scratch. Once the first scratch is there you stop worrying about it.
Once you put down the first sticker I imagine that worry goes away. I think getting a tattoo is still an insurmountable problem for me personally, but I get it.