It's easier to go downhill than to climb uphill, so it's easier to fall into bad habits than into good ones.  

    Bad habits do not come suddenly. They come little by little without one's being aware of their danger. Schoolboys first pick up little bad habits at school and on the street. When they cannot write their lessons, they copy from their schoolmates. If they see older（年纪更大的）boys smoking, they also want to learn to smoke. If they see their friends gambling（赌博）, they want to gamble. When they get older, the habits become stronger and stronger, so that they can no longer get rid of（摆脱）them. From copying, they learn to steal（偷窃）; from gambling, they learn to cheat（欺骗，行骗）.

    How necessary（有必要的） it is that we get rid of the bad habits at the beginning! Or they should overcome us in the end!

—Yes, and the bird has two wings __________two legs.