For me I often feel stuck when I think of how permanent a tattoo is. I see a lot of cool designs that I like at the time but when I start thinking about the having it permanently done I start to change my mind and look for something else.
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Another approach is to visit tattoo studios in your area and look at the designs and photo displays on the wall or their album to search for inspiration, but keep in mind, don't limit your imagination to what someone else already has, be creative.