Coupon Rate 8%
yield to maturity 10%
maturity 5 years
face value 1000$
Price 924,1842646 $
Coupons annually

the durations turns out to be 4,2814 years under my calculations.

Now:
1) i read the durations is the time needed to get the price of the bond paid back. But i do not get it, since at time 4,2814 years i only got 4 coupons of 80$ each and so a total of 320$ which is ways less than the bond's price (924,18$)
- do you know why is that? do you know why at duration time i don't get the price paid off?

2) i studied that selling the bond at duration time is the best off. Do you know why?
furthemore, if duration changes over time, how can i sell it at the duration time ? should i consider to sell it at the beginning duration time? (in the latter example 4,28years)