Cause Of Low Yield In Experiment

The mass of aspirin is 1.4791g and the theoretical yield is 2.61g.So, the percent yield is 56.7.Why is the yield not as expected 100.I so far have that not all the aspirin was put into solution when ethanol was added.There could also be some leftover impurities though i dont know if this is actually right.Thank you for the help.