"laziness"

Hello /sci/,
Could you explain to me why people are willing to go out of their way "to be lazy".
Examples:
  Walking an extra 20 feet to the automatic door instead of pushing open the other door.
  Waiting an additional 5 minutes instead of going up a flight of stairs.
I'm sure you've observed others. Is it just a habit people get into? Has there ever been a study into this.

When you are surrounded by evil, do good; when you are pilfered by greed, be charitable; when you are embraced by sorrow, be strong; when others give up, be relentless; when you are surrounded by death, bring forth life; and when others tell you what to do, make up your own mind. This is the power of your choice. You a...re the language of that voice. The question is, Will you speak? Everyone else says no. >:3