It is the exact same thing as saying it is impossible to be guided by Christianity because there is no time to read through the Old and New Testaments (Bible).
2.) Actually, one already had the entire human civilization previous to them to experience and learned what specific actions lead to what as a result.
a.) The past human civilization had already learned and experienced what it’s coined to possibly be “common sense” today; what is good and bad judgement and what we should be cautious about.
b.) Then, what they learned from that would be what determines the morality of life.
3.) But even with all this time that passed and this knowledge that one already has, the ethics one already has doesn’t mean it is always right; one still has more to learn about the effects of actions on one’s general happiness.
4.) Compared to sailors who goes to sea with the National Almanac already calculated, so does other rational living beings who go through life with their minds being sure of simple questions of right and wrong and more complex ones of wise and foolish.