Why is it important to have a high intrest rate for an investment and a low one for a loan?

Investment is an act of setting some amount side to grow and accumulate in the nearest future ... Investment is quite different from savings so Higher interest rate on investment is very important because tends to act as an aiding factor in letting such investment yield a lot of profit and grow.

While loan on the other hand is debt borrowed that has not been paid back, people lend money for so many reasons and they do this because they don't enough capital so they source for external fund, but in the situation where interest rate accrued on loan is high, then it will be difficult for such individual to pay back because this will increase the money that has to be paid back.