pre-noun adjectival
reasonable; natural; understandable
Used to express that something is only natural or understandable under the circumstances. Often appears in the pattern 無理からぬことだ or 無理からぬ話だ.
It's only natural that he would get angry.
It's understandable that a beginner would make mistakes.
Derived from 無理 (unreasonable) + the classical negative auxiliary ぬ (not), literally meaning 'not unreasonable'. The expression has fossilized as a fixed pre-noun adjectival.