What does the phrase 'genes must be expressed' mean

"Genes must be expressed before they can influence behavior"
What does this mean? Please help!

Gene expression = the gene is active = the gene is "turned on" = it's currently being transcribed from DNA to RNA to Protein.

NOTE that not all genes code for proteins tho. Most genes are regulatory in nature, they specify the conditions under which other genes are supposed to be active (or not active). For example, when "gene A" is active (being expressed), it goes on to influence the expression of "gene B," which may go on to influence the expression of another gene or protein.

The expression of a gene is when its protein is made or transcribed. The protein must be made before it can take effect