“I’ll look it up later” is where good questions go to die.

Questions have a short half-life. The curiosity that made you want to know is attached to the moment, and once the moment passes the question loses its charge and joins a long list of things you were briefly interested in. Deferring is not really deferring, it is a polite way of declining.

Look it up in the thirty seconds while you still care, even if the answer is shallow. When that is genuinely not possible, write the question down rather than trusting yourself to remember. A list of unanswered questions is one of the more useful documents you can keep.