Very true, selling t-shirts   are not considered as passive  income  hence you would need  to put efforts in able to sell some  of it. This means  you would  still need  to work and  convince  people  and advertise  about  your certain products. Passive  income means   its fully automated  and  you still gaining  money without  doing anything and this  could be achievable   by having  good  investments  or businesses  here  on  online  world  or on  physical world.