> What if you have a grid of 30 item, do you press 20 times tab to focus finally the item you want to interact with?

If this grid a central component of the application and navigation inside it is very common, I would argue that there should be a way to quickly move around the cells. The "how" is up to the specific application and the paradigms it promotes. For example, line navigation in vim is possible with "<N>G", but such a shortcut would seem absurd in another application.

- Underlined letter: Alt-<letter> takes you to that field.

- Spreadsheet-like stuff: arrows, PgDn, PgUp, Home, End, … move inside of it.