Player inventory double click to choose items?

I have played this game last 2 month ago. Today i found out, if i want choose an item in the players inventory, i must do an double click? No longer one click? WHY?? Wtf?

Omg :scream: NOOOOOOO

Oh No No No a double Click !!! My hand is now broken all because of the double click. Just please tell me what does it matter