At what point is it not worth repeating a start up idea on another continent?

With continents being North America and Europe.

The scenario is:

1) You have an idea

2) You do your research and you find it is a valid idea (including researching possible competitors etc.)

3) Only at a somewhat later stage (just before presenting to possible investors for example), you find that your idea has already been implemented on the other continent and it is one year ahead of you, it's doing well and you did not find it because it is just picking up now and / or had a weird name (or other) but already has paying customers, a lot of funding and a growing team.

Worth carrying on? What is the threshold?