What to do when stuck
Recognize and accept you are being stuck.
Think of being stuck as as honourable and positive state, from which much can be learned.
Express your feeling with RUBRIC words, so that you can distance yourself from the state of being stuck.
Record as clearly as possible what is blocking you.
Return to the Entry phase and reassess KNOW, WANT, and INTRODUCE.
Do more extreme specializing with more drastic simplification to detect a pattern.
"if you can’t solve your current problem, alter it until you can."
“If you can't solve a problem, then there is an easier problem you can solve: find it.” by Polya
Pretend you explain the problem to your friend with clear description, specialization, conjectures, and counter-examples.
Find out unnecessary hidden assumptions.
Be a good questioner, and investigator.