关于skewness：A positively skewed investment return m

关于skewness：A positively skewed investment return means there were frequent small losses and a few large gains. Negatively skewed means there were frequent small gains and a few large losses. 想问下这句话要如何理解呢？如有一个分布是右偏的 但全部在纵轴的右侧，这个不就是不成立了吗？