Desings that solt and designs that did not

I funny a i keep going on this 3d printing journey in my area i had request for stuff that i never thought would've be designed and the stuff i thought hey this is super popular  this would sell did not, like for example when K-Pop demon hunters came out I thought the huntrix and sasha boy light box and the light sign they they had i the movie would be popular but did not sell a one i designed and printed off this  little loop de loop boomerang thing for may grand kids and sold 300 of them to a teacher.  i am definitely figuring out the demographic around my area