Answer:
Short answer is primers are partially complementary.
Step-by-step explanation:
Forward primer: 5'-AGTCTACTCGTAACCGGTTACC-3'
Reverse primer: 5'-TAAGGCATCATGGTAACCGGTT-3'
When we write reverse primer 5' to 3' we can easily see that
3'-TTGGCCAATGG---5' is complementary to the forward primers'
5'---AACCGGTTACC-3' sequence. So instead of binding to the template DNA these primers might bind each other resulting with reduction of efficiency of DNA amplification.