Why can't we choose a card?

[msoong]

Asking for my wife, who never played the boardgames but loved the BGA implementation:

When she picks minor/major improvement space (in a solo game), some occupations can not be chosen for some reason (even though she has enough food to pay for it). Is there some rules we are not aware of?

[Ranior]

The yellow Occupation cards can only be played via "Lessons" action spaces.

The orange cards are Minor Improvements and can be played via improvement actions.