For example, Boromir falls under the influence of the Ring
and tries to take it from Frodo.
When he realizes what he has done, he is grief stricken, and gives his life defending the
other Hobbits to atone, and dies with his honor restored.
Frodo ignores Gandalf's warning to never put on the One Ring, and puts it on while being besieged by the Nazgúl. For this error in judgement, he earns a wound that will
never fully heal. Later, when he decides to keep the Ring rather than casting into the
fires of Mount Doom, he loses a finger as Gollum takes the Ring and fulfills the plan set
in motion.
There are numerous other examples in the books as well, such as Beregond's decision to abandon his post and subsequent submission to Aragorn's judgement, Eowyn's decision to abandon her post and come with King Theoden to the first battle of Gondor leads to her being wounded emotionally by the Witch-King, and others.