Meaning of the word "he that stays in the valley will not get over the hill" in English

What does "he that stays in the valley will not get over the hill" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

he that stays in the valley will not get over the hill

US /hi ðæt steɪz ɪn ðə ˈvæli wɪl nɑt ɡɛt ˈoʊvər ðə hɪl/
UK /hiː ðæt steɪz ɪn ðə ˈvæli wɪl nɒt ɡɛt ˈəʊvə ðə hɪl/
"he that stays in the valley will not get over the hill" picture

Idiom

one who is unwilling to take risks or leave their comfort zone will never achieve success or overcome challenges

Example:
You need to apply for that promotion; he that stays in the valley will not get over the hill.
I know starting a business is scary, but he that stays in the valley will not get over the hill.