Fajing is not always about generating power.
Sometimes its just timing. Using timing means to listen, or perhaps to probe to elicit a response, then allowing the response to be heard, understanding what the energy feel is saying and exploiting it.
Fajing can also be about to use your partner’s weakness against him.
For example, if he tries to enter without a proper root then he has already unbalanced himself. All you have to do then is to get under him and launch him the moment his energy is receeding after he tried to use it.
This is why my teacher from the Wei Shuren lineage doesn’t teach fajing on its own. Instead, he stressed learning the principles embedded in the form. His explanation is that when the principles fall into place fajing will happen.
Otherwise, if you learn fajing separately from the form when you try to use fajing it will look forced. You will also not be able to use it naturally as part of your arsenal of techniques, creating a feel of fajing is fajing and technique is technique, instead of fajing and technique is inseparable.
One reason why we don’t always have to fajing hard is because to fajing hard is like spending money unnecessarily, except in this instance you squander your strength and energy. Instead, use only as much as you have to and fajing then becomes a fun, relaxing exercise.