Apply Data Validation If Cell Value Is < X

I'm building some work life balance spreadsheets for employees to show satisfaction levels / hours etc...

For the satisfaction piece - users will enter a value between 0 and 5 with 5 = happy as larry and 0 = ready to quit. Next to this field is a comments box. This comments box only needs to be populated (from a data validation list) if the staff are unhappy.

I need the file to prevent users entering a value less than 3.99 without selecting a comment from the validation list. Users will go into the file and update for their own lines so the check can be written into the save function maybe???