Starting my 3rd product store, have a question

Hi guys, how do you all choose which markets to go into? Like fashion, supplements, beauty, whatever.
I did my first product in the pet niche. 2nd in the supplement niche. Both flopped. But my point is, how did you all decide on which niche to target, or which market to target? Or do you guys not target only 1 specific niche?

Do you do 1 beauty product and then do a supplement product next?
Thanks!