Aside from the celebrity trend, part of the appeal of small, fine line tattoos is that they are quick to do and easy to hide. As opposed to a larger full colour piece, for example, which can take hours a mini tattoo will take much less time and is easier to hide. Its your secret if you want it to be.
If you are scared its painful then what would be better than trying a small fine line tattoo If it is painful, at least it won't be painful for long! Starting with a micro fine line design also gives you a chance to see if being tattooed is something you like.
If you are a bit unsure about it, getting something small and fine is a good way to start.