Does Long Term Investment Help??

Any News Channel or Paper I view tells that everybody can get benefitted with long term investment. I am not sure what thay mean by long term. For example if somebody has started investing in mutual funds say 1.5 years ago I believe right now he will be in loss calculating current market condition. Do you think 1.5 years is not long term whereas if somebody who started 1.5 years ago but sell all his units 1 year ago will defenitely be in profit and I believe .5 years is defenitely not long terms. I believe its all about investing 30 minutes or so everyday to keep you updated and make your selling buying decisions. Experts comments please...