Lies are difficult to understand (7)
I believe the answer is:
realise
'understand' is the definition.
(I've seen this before)
'lies are difficult' is the wordplay.
'difficult' indicates an anagram.
'lies'+'are'='liesare'
'liesare' with letters rearranged gives 'REALISE'.
'to' is the link.
(Other definitions for realise that I've seen before include "Get the idea?" , "Make concrete" , "See the light" , "catch on" , "Achieve; turn into cash" .)