Characters
Grep and Grok are stand-ins for complementary aspects of human intelligence. Grep is the tool for perfect match. Grok is the tool for pattern recognition.
Grok is really bad at thinking through all the possible matches but when it sees one it know if it's wrong or right instantly. The more Grok has to do and the more precision is required the more mistakes it will make.
Grep on the other hand will tireless go through vast amounts of information and find accurate matches based on any combination of criteria. As long as the criteria are formal and can be expressed through "a = a".
You can ask Grep to find all the matches of "cat" in a text. But you cannot ask it to find only "cat" only when it is used metaphorically. Grok will start loosing track of "cat" after a few paragraphs. But it will instinctively know the difference between "I have two cats and a dogs" and "it's raining cats and dogs".
Most people don't have a good intuition about when they grok and when they grep.
Grep excells at exact matches, long searches, and can always be relied on when asked if a string is there or not. But ask Grep the difference between 'duck' and 'duck!' and all you will hear is 'one has an exclamation point.
Origin: Unix search tool
Grok looks at the situation, notices the surrounding cues, and gets the point immediately. But give Grok complicated rules to follow and you will get a lot of mistakes
Origin: Grok origins