look at from their point of view - they are not there to help you, they just want someone to perform a role who that can be sure can actually do it - they are not obliged to hire you and train you up, at their expense.
if you were hiring and you had two applicants - both sounded more or less the same, except one has done it before and could just start right away and be up and running on the first day, and you can go off and get on with other work and trust him to get on with it ... and the other would need an assessment, training, practice and possibly a test, and then need to be monitored.
both would be on the same wage
who would you hire?
you would pick the person best suited.
sounds like you need to get some work experience, or a trainee position.
you can't expect companies to give you a job just because you reckon you could do it.
regarding the forklift - sounds like it could be dangerous so you have very little chance of getting that job if you have never done it before - again you need to be a trainee