Since it's damned difficult to turn off gravity, the astronauts on earth train in a huge swimming pool while wearing the suits they will wear when in space or on the moon. This allows them to experience conditions similar to, but not identical to, those found in their work site.
Remember too that they're wearing a personal HVAC system on their back as well as comm gear and an oxygen supply. Lunar gravity is only about one sixth of Earth's but all that baggage would make anyone a bit clumsy.
Psychology plays a part in your performance too. You look up in the sky, see your home planet and realize you're a quarter million miles from home and your only chance to get home is a glorified tin can built by and inspected by folks who remain safely in their beds regardless of what happens to you.
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