The two failure modes
Reminding fails by being weak: 'be careful,' 'remember the rule,' 'don't forget X.' The model nods and proceeds. Steering fails by being noisy: long preambles repeated every turn that the model starts to ignore. The cure for one is not the cure for the other.
Steering changes operating state
A steering note has a structure the model can act on: what changed, what is now canonical, what is now forbidden, what is the next safe step. It can be checked against future actions. A reminder cannot.
Compress reminders, expand steering
If you find yourself reminding the model of the same thing every turn, that thing should move to the spine (where it lives once and binds always). If you find yourself steering across many topics, compress to a structured list — bullets and short rules survive long sessions better than paragraphs.