Gravity is great, you drop something and it will gather at your feet ready to be picked up again and doesn't float away above the trees never to be seen again.
Of course it isn't so good if the thing you drop is a hammer or a priceless vase but you get the idea and over the past 2 million years (or 6000 years if you are a Bible reader) human life has been evolving on Earth and gravity has defined our size and shape as well as keeping us rooted to the ground.
As we are a product of gravity, problems occur when you take it away as our astronauts find out when they leave the safe embrace of the Earths gravitational field and venture out into Space.
Once gravity is removed the human body goes to seed, our bones and muscles waste, the heart shrinks and changes shape while hand eye coordination is shot to bits and the bodily fluids float around inside the body bringing dizziness and an almost constant feeling of nausea.
A short trip to the moon and back would take four days out, a day or so bumbling around planting flags and hitting golf balls and a four day trip back, you could be out and back within 10 days and the effects would be minimal.
Those returning from longer stays on the International Space Station are greeted by Gravity and a hospital worth of medical services and that's where the manned missions to Mars hit a stumbling block.
A trip to Mars would be a minimum of six months to get there, and the same to get back again. Due to the orbit of Mars around the Sun an astronaut would get either a 30 day window to return or wait until the next time it comes close to Earth which is 18 months later so even the shortest trip would mean 13 months in less gravitationally favourable circumstances or 30 months for a longer trek.
As it would be impossible for an astronaut to collapse into a hospital trolley on arrival to the red planet, they would be 240 million miles away with just a first aid kit and muscles like jelly which isn't ideal.
All which makes the talk about Mars Missions far fetched until science develops some form of artificial gravity aboard the rockets or we get a fully equipped hospital built up there first.