Talent is 98% hard work - even Brel said so. The best signal for lack of talent is therefore quite simply low production. That does of course not mean high production guarantees talent, so something does exist that needs to be present - what is that? Talent and Drive - both are quite useless without the other, but what exactly is 'talent'? I would say its a form of the unconditioned: in some people it survives, even unto old age. Some learn to focus it on a particular craft. But without drive, it still goes nowhere.