It's just the desire to have something you don't yet have. It's usually irrational and it probably doesn't make you as happy as you first thought it would when acquiring the thing you GASsed for after a few days.
Try reading up on Buddhism and practicing thriftyness. Read about poverty. It costs 30p to prevent someone from going blind (that stopped me buying mars bars).
You could try the thirty day trial - as in, if you still want something after a month, then consider buying it.
Maybe if people stopped hoarding, they'd use less trees.
Find beauty in simplicity. Grass-roots (uprights) and unbranded amps.
Then read about Buddhism again.