From page 244, PHB - description of the 5th level spell Geas:
You place a magical command on a creature that you can see within range, forcing it to carry out some service or refrain from some action or course of activity as you decide. (...) While the creature is charmed by you, it takes 5d10 psychic damage each time it acts in a manner directly counter to your instructions, but no more than once each day.
So my question is what will happen if some monster casts Geas on a player and succeeded, forcing him not to attack for example. As I understand the description although player failed his saving throw he CAN disobey the command but he will take 5d10 dmg. And if he survives it he can now disobey it as if the spell was not there? He can take dmg only once a day.
From page 278, PHB - description of the 2th level spell Suggestion:
(...) The target must make a Wisdom saving throw. On a failed save, it pursues the course of action you described to the best of its ability.
The wording of Suggestion spell does not give any way for charmed creature to disobay.
And if I understand it correctly how to describe to the player under the spell the difference between those two spells? If a creature casts Geas how to tell the player that although he's charmed he can disobey but with consequences? :)