a fox may grow gray, but never good.
江山易改，本性难移。
a friend in need is a friend indeed.
患难见真情。
a friend is easier lost than found.
得朋友难，失朋友易。
a friend is never known till a man has need.
需要之时方知友。
a friend without faults will never be found.
没有十全十美的朋友。
'after you' is good manners.
“您先请”是礼貌。
a good beginning is half done.
良好的开端是成功的一半。
a good beginning makes a good ending.
善始者善终。
a good book is a good friend.