In the end man got them from 501 to 51 being assiduous and hard-working (8)
I believe the answer is:
diligent
'hard-working' is the definition.
(I've seen this before)
'in the end man got them from 501 to 51 being assiduous' is the wordplay.
I cannot really see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'man' could be 'n' (knight, a man in chess) and 'n' is located in the answer.
'from' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'501' could be 'di' (501 in Roman numerals) and 'di' is found within the answer.
'51' could be 'li' (roman numeral) and 'li' is found in the answer.
A single letter 'g' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'and' acts as a link.
Can you help me to learn more?
(Other definitions for diligent that I've seen before include "I tingled, being hard-working and meticulous" , "Attentive and busy" , "I tingled, being hard-working and conscientious" , "Thorough" , "Putting care and effort into work" .)