οἶσθ' οὖν ὃ κάμνει τοῦ λόγου μάλιστά σοι
From LSJ
Μοχθεῖν ἀνάγκη τοὺς θέλοντας εὐτυχεῖν → Laboret is, beatam qui vitam cupit → Sich abarbeiten muss, wer glücklich leben will
English > Greek (Woodhouse Quotes Reversed)
know you what part of your tale halts the most, know you what part of your tale is weakest