The Small Freedom of an Undo Button
An undo button offers a modest kind of permission. A person can try something, see its effect, and change their mind without treating the experiment as a permanent commitment.
This matters because an interface is often learned through use. Instructions cannot anticipate every moment of uncertainty, and a warning before every action can make a simple task exhausting.
Reversibility provides another form of protection. It reduces the cost of a mistake while preserving the person's ability to proceed.
Some actions cannot genuinely be undone. A message may already have been read, or a consequence may have passed beyond the system. In those cases, the limit should be clear rather than hidden behind reassuring language.
Where reversal is possible, making it easy is a small act of respect for ordinary human fallibility.