It is ok to plan for a career in an industry that is not expected to grow very much or even shrink a little over time

It might or not be ok to plan so, depending on certain circumstances.

Explanation:

Feasibility to Plan a career in an industry, not expected to grow much or even shrink

It is ok to plan so, as the industry growing less or might shrink - will attract less entrants into it. So, less entrants might imply less competition, which might be a favouring opportunity for the firm. Also, a little innovation might act as a catalyst for growth of a less crowded industry.

It is not ok to plan so, if the industry is anticipated to be outdated or irrelevant in constantly modernising businesses. Also, if the industry lacks scope of innovation & further upgradation. As, in both these cases, the lack of competition (as mentioned earlier) will go futile.