Prov. 23:13 says:
Whoever conceals his transgressions will not prosper,but he who confesses and forsakes them will obtain mercy.
‘Prosper’ means to ‘succeed’.1 The proverb is saying that people who try to hide their sins will not succeed (the inference is that they will be found out, even if they try to hide their sins — nothing is hidden from God, after all: 1Cor.4:5), but people who confess their sins will be given success.
One of the morals of the proverb is that you don’t have to pretend to be righteous in life; you just have to be humble enough to admit your faults — if we do this then God will make us succeed, even though we are sinner.
1. Compact Oxford English Dictionary entry: prosper