Ideally you literally keep your bare hands out of your tank as much as possible. Its a way to introduce foreign substances. But it can also be applied more philosophically, like don't constantly tinker etc...stability is paramount.
It means stop constantly adjusting things in your tank. This applies to light settings, parameters, moving corals, etc. Try to keep everything stable so your livestock can adjust.
Every time you put your hands in the tank, it is an opportunity for error (dirty hands, knock something over, scare a fish to jump out, accidentally spill water on electric components, etc....). Therefor, the less often hands go into the tank, less opportunity for error.
Yes, at times u have to go in the tank. That’s just part of the hobby, maintenance etc. For me, it’s planning and placing corals accordingly (coral type, growth pattern, aggressiveness) and letting them fill in the space over time. Takes time for them to settle.
It means to leave your tank alone. It should be able to go weeks without you doing anything other than testing and cleaning the glass. Leave it alone and let it grow.