Why is it so hard to define viruses as living or non-living?

Viruses are not always classified as living cells because they cannot live independently. They rely on a host to provide all resources to live, without a host they are in a dormant, near dead like state. Therefore it has to define a virus as dead or alive as it may or may not have a host.

Virus are living beings but it is hard to decide whether they are living or not because of several reasons. 1- they show the characteristics of living being when only it live in a cell. 2- they never breathe 3- they are minute 4- they have a simple body structure 5- they reproduce some say they are in the border between living and non living