After a failure, one has to be tolerant (10)
I believe the answer is:
permissive
'tolerant' is the definition.
(thesaurus)
'after a failure one has' is the wordplay.
'after' means one lot of letters go next to another.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'failure' becomes 'miss' (miss is a kind of failure).
'one has' becomes 'I've' (contraction of I have).
'per'+'miss' is 'permiss'.
'permiss'+'ive'='PERMISSIVE'
'to be' is the link.
(Other definitions for permissive that I've seen before include "Showing indulgence" , "granting authorisation" , "Free" , "Like our society" , "Liberal, broad-minded" .)