Hearsay evidence is evidence of what some person, other than the witness, has said (on some other occasion), where the purpose of recounting what was said is to establish the truth of what was said (as opposed to the fact that it was said).
Legal practitioners easily forget how arcane it is to do what they do. When the time comes they recognise one thing; giving evidence is intimidating.
It’s easier to forget than to remember. If a witness has forgotten things it is permissible, sometimes, for the witness to check a written record of what has been forgotten.