Lactose (or rather, its derivative allolactose) can lift the Lac Repressor protein from the Operator site in DNA, thus allowing for expression of the genes coded by the Lac Operon.
However, lactose cannot cross the bacterial cell membrane without the help of the Permease protein channel, which is coded by the lacY gene in the Lac Operon.
So, it appears that we have a case of "what's first, the chicken or the egg?" - how can lactose enter the cell and allow the expression of the lacY gene, if the Lac Y gene needs to be expressed for lactose to enter the cell ?
Using your own 150 or fewer words, how could you explain this apparent conundrum?