The esters and water have significantly higher boiling points
than the ethanol, which makes it impossible to remove those
compounds from the equilibrium by simple distillation.
A larger excess of ethanol (a five-fold molar excess) usually
causes problems in the phase separation later on. Thus it would
have to be distilled off before the workup.
Water is one of the products in the Fischer esterification.
Thus, any water in the system due to wet reagents, wet glassware,
etc. will reduce the yield of the ester because the equilibrium
will be shifted to the left side.