My neighbor is a hoarder. Many animals hoard by nature, and they say human hoarding may be related to that but there is substantial evidence lacking there.
My sister and her husband are both hoarders of things.  they love to buy in bulk and just continue to keep everything they buy therefore their house is full of stuff
That kind of behavior has been associated with health risks , economic burdens, and adverse affects on loved ones. It's unfortunate.
It is very unfortunate.  We have helped them a few times clean their house but it just gets full again so it seems somewhat pointless
It's not easy for us to understand, but hoarders really do have a feeling of attachment to these items they collect. 
yes, it is hard but I do try to talk to her and figure out the underlying issue.  I am the complete opposite end of the spectrum and I like to throw everything away and have things neat and orderly
houses may become a fire hazard (due to blocked exits and stacked papers) or a health hazard (due to vermin infestation, excreta and detritus from excessive pets, hoarded food and garbage or the risk of stacks of items collapsing on the occupants and blocking exit routes).. Hoarding affects more than just the person who has the strong attachment to possessions, as other people living in the home and neighbours can be affected by the clutter. Individuals with hoarding disorder have a quality of life as poor as those diagnosed with schizophrenia
) One theory suggests that human hoarding may be related to animal hoarding behavior, but substantial evidence is lacking.
Human hoarding.
Civil unrest or threat of natural disaster may lead people to hoard foodstuffs, water, gasoline and other essentials that they believe, rightly or wrongly, will soon be in short supply. Survivalists, also known as preppers, often stockpile large supplies of these items in anticipation of a large-scale disaster event.
Human hoarding Anxiety disorder and hoarding.
Individuals who meet diagnostic criteria for hoarding