The truth is, it could be very difficult for one to ask for money borrowed to a friend. Matter like this has resulted to serious disagreement which has spiralled into endless enmity. It is not wise for a friend to borrow money to a friend he knows he can't pay back. The main reason why a friend might not payback the borrowed money to him could be because of the friendship existing between the two of them.
Personally, I have learnt basic rules of borrowing out money to anyone, which is never give out money you know you cannot let go. And I have used this same principle in dealing with every area of my finance.
As of recent, a neighbour came to me for me to borrow her a certain amount of money, and all I did was to tell her I don't have the exact amount she requested for, but I can only borrow her a lesser amount, which she agreed. Luckily for me, she failed to pay back the money as agreed, and due to the principle of borrowing I applied in dealing with her, I didn't feel offended with her refusal to pay back.