Why cannot fertilisation take place in flowers if pollination does not occur?

Explanation

In a flower, fertilisation requires both male and female gametes. So, it is necessary that the male gamete reaches the female gamete. This can happen when the pollen grains are transferred to the stigma through any means of pollination.
Hence, fertilisation cannot take place in flowers if pollination does not occur due to absence of pollen, (i.e., the male gamete).