Bitcoins sustainablity

People may disagree however, I personally think bitcoin is fully sustainable and has huge potential. With typical currency such as the Euro there is a set amount, this restricts the supply which when mixed with demand determines the value. Furthermore, with bitcoin their is a set amount (21m) Which means demand will always increase however, supply will decrease. Supply will decrease because people overtime lose their bitcoins either through human or machine error. Going by this, it is potentially possible that bitcoin could eventually have a very small supply.