A lot of people think we'll live on Mars someday, and possibly someday soon.  These people are idiots.  Here's why: 
  1. Mars ain't got no air.  Air-breathing humans would have to either constantly wear ventilation masks or live in pressurized bubbles.  It would be like living underwater.  All the time.  Forever.
  2. Mars is fucking cold.  I feel like this point gets overlooked a bit because Mars is in the "habitable zone" i.e. there can be liquid water in some places sometimes.  But a summer day can swing from 70°F to -100°F.  That's a negative sign there.
  3. There's no sun.  There's some law of physics that relates the sun's power output to the distance a planet is from it.  Mars is farther from the sun than Earth.  Less sun means less heat, less solar power, less plant energy, less everything.
  4. Mars ain't got no stuff.  Stuff like water (ok there's some), plants, animals, building materials, factories, fast food establishments.  Point is, you'd have to bring literally everything you'd ever need for anything.  Yes you can 3D print some stuff, and yes you can maybe grow potatoes in your poop, but for the first many years of settlement there you'd have to come with your bags packed.  People underestimate how ridiculously difficult and expensive it is to shoot a rocket from Earth to Mars.  Yes it's been done before, but it's kind of a big deal every time it happens.
  5. We're not gonna terraform it.  Yes it's hypothetically possible, and hey we've terraformed Earth so it can't be that hard.  But the amount of energy required, and the international (interplanetary? intergalactic?) agreements it would require, and the choice of the best actual way to terraform, means it'll never happen.  It's a science fiction idea.
Earth is really good at sustaining human life.  It has the gravity we're used to, the air pressures and chemical components we enjoy breathing, the temperatures we can deal with, and the food we like to eat.  Maybe instead of trying to terraform a planet that has none of those things, we could try to make our current planet a little better. 

Many times throughout history, an unwise person made a proclamation about the future that turned out to be utterly false.  Perhaps I'm that unwise person. #science