(PW) start from the beginning so you’ll have full advantage of any favorable outcome.
He is a very wealthy man. He was one Microsoft’s first employees and got in on the ground floor.
(UsingEnglish)
If you get in on the ground floor, you enter a project or venture at the start before people know how successful it might be.
(free)
get in on (or start from) the ground floor Informal
a. to enter a business, organization, etc., at the lowest level
b. to be in a project, undertaking, etc., from its inception
(your)Informal
The beginning of a venture, especially regarded as a position of advantage: investors vying to get in on the ground floor of a development project.
